Ok, I ripped out all the plugs and still Sonar hangs.  The only thing I have left is ONE DXi wrapped in Directixer (Superior Drummer).  Fails with either Superior 1 or Superior 2 so I don't think the DXi is the issue, unless it is the wrapper (Directixer) that is responsible.  But I have no safe/easy way to eliminate that variable at the moment.
 
I'm going to next try a painful start/stop test sequence but not moving the mouse away from the focus of the area where the transport buttons are and see if that makes a difference.
 
I'm also a bit suspect about MIDIYoke being loaded, even though it's not being used, so to speak.  Not sure if maybe I should risk trying to disable it in the devices view.
 
Yes, I have separate OS and Audio disk, always ran that way before no problem.  But that was on a W2K single-CPU/core system.   
 
I just compared another hang dump and it's darn near identical, whatever is happening is the same thing, at least that much is encouraging - meaning it is indeed ONE CONSISTENT problem.
 
I could re-locate the audio disk drive onto the same Primary IDE Channel as the OS drive as long as it isn't going to confuse Windows and end up muck something up in a domino effect.  IIRC my thinking was to make use of separate IDE Channels to reduce any potential conflicts or the two disks competing for use of the same IDE Channel.  Keep in mind, I'm using SATA drives, however the BIOS is configured to run in IDE legacy mode, on purpose so I don't have to mess around with SATA drivers, slip-stream, etc.  System is blazing fast for my needs so I'm not remotely concerned about hypothetical speed limitations compared to running in true SATA mode.
 
Sonic

Windows doesn't handle disk read/writes very well, and the older the system, the worse it gets. The old IDE-based pro-multimedia systems (and servers) usually had a hardware disk controller managing all data io disk read/writes (instead of Windows). I know that having a separate audio disk is a great idea, but on an old system, it needs to be configured perfectly for it to work flawlessly. Ultimately, it's easier to put everything on the same physical disk.

Plus those dump files are 90% useless.  Unless your one of the software vendors with the error code decoders. Or can read raw memory dumps.

If I understand your system correctly, you have 2 separate physical HDDs, both ATA/IDE (PATA not SATA). The 2nd disk, which is your Audio disk, is shared with the CD/DVD drive (PATA)? That's not ideal.

If so, I would test by first saving a small Project (w/ audio files) as a Bundle, then copying that over to the disk where the SONAR Program Files are. Hopefully your SONAR Program Files are on your OS disk, as well as your other soft-synths & FX, etc. that are accessed by SONAR.

There some other conflicts I faintly recall relating to PATA HDD ports. And ISA mice. Try that small test above first before ripping your PC apart.

Okay, I just reread your edited post. You have SATA drives running in IDE legacy mode (set in the BIOS). Make sure your mobo has the right chipset drivers installed.

Yep, all chipset updated.  Believe me, I knew building a "new" W2K/XP DAW was going to require getting a lot of specifics correct so I spent months on the project.  That's what so frustrating.  My gut still says it could be a service pack issue.  SP2 and SP3 came out AFTER all the software I am using and I'm worried maybe there is a runtime library incompatibility.  The dumps are useful in the sense they show what was being executed (by looking at the stack) and the same sequence is occurring leading up to the hang, stuck on the same event object at the same place in the code.   I'm wondering if I should just bite the bullet and spend weeks rebuilding the system and rolling back to W2K SP4, which I know for a fact works.  I wanted XP because Superior rummer 2 had some fairly important patches that won't work on W2K. But I can live with those bugs over a complete Sonar hang if need be.   The only other thing I'm thinking is maybe I installed something this time around in S5 that I hadn't before, which is possible.  Some synth or something that is mucking things up?   Maybe I should try outright excluding any Sonar synths and VST's, like Groove Player, Perfect Space, etc. and see if they has anything to do with the hang.    
 
Sonic
 
 

Ugh...too early to be sure since more testing is needed tomorrow, but it seems as if there is some dynamic involving Directixer.  I turned on the Fixed Buffer option for Superior Drummer inside Directixer and as of yet haven't been able to get Sonar to hang.  BUT now the machine freaks out when I have other things in the Synth Rack - and sometimes even when I don't.  CPU goes red and massive popping and sometimes screeching.  And can't even get it to stop by disengaging items in the Synth Rack, have to close the whole project. I just can't imagine what is the root cause of all this lunacy.  I still go back to the fact it feels like some kind of quirk related to incompatibility between XP SP3 and the other DAW software because none of this baloney happened on W2K SP4.
 
 
 

You do have a chioce
Stay were you are stuck in the past with all the issues that we well remember from those days wasting your time trying to make it work properly. 
Or come into the present where we can help you sort things out and start making music. 
This would cost you the price of a computer that has at least W7 and 4 GB of RAM. In my town they sell for $50. As said, the software is now free. 
You are almost all alone in your world of hanging on to the past. 
It's a hobby but most of use over time dole out the money to at least try and keep up with the technology as it upgrades. I tend to stay back a few years my self and my computers are all outdated but they are more than enough for my simple needs. 
I say this in a kind way because I see your posts over and over and my only advice would be to at least think about at least moving out of XP 32 bit. How much time are you willing to waste fighting that outdaated system? That time could be well spent learning the newest software. 
 

Red herring, the Fixed Buffer setting in Directixer causes havoc and hangs as well.
 
The hang only occurs after stopping, not when starting, not while playing/recording, not while editing.  What is it about stopping the friggin' transport that is so special it could be the root of all this ?!
 
Anyone ??
 
I may have to buy another disk (was thinking about doing that anyway as a backup) and make an image duplicate so I can try more extreme theories/troubleshooting without risk to the current disk.
 
 

None of my business I guess, but instead of buying another disk why not buy a Win10 computer ? 
I think it will be problematic to get help on systems as old as XP. It is not even a supported ( by Microsoft ) going back 3-4 years.
 
 

Going to a newer OS is not the answer, in 2 or 3 years the same paradigm will just repeat itself and there will be people saying to upgrade again.  There's absolutely nothing conceptually wrong with an W2K/XP box and slew of software designed to run on it. All of which I already know well and own, along with all the compatible hardware and drivers. Which I can keep running and servicing for many, many years to come.   There's just one maddening intermittent quirk hiding someplace in this new DAW that needs to be figured out.

I was pondering testing the Superior 2 Drummer VSTi using the cakewalk VST Adapter in S5 instead of using Directixer......but I'm not sure what will happen.... can VST's that are wrapped by Sonar VST adapter be completely "removed" using the plug-in manager? Or rather once they are scanned & added does Sonar basically have them permanently installed in the OS somehow?  Asked another way, is this something I could test and easily "undo" or would I end up committed somehow with Sonar or the OS and not be able to easily get back to where I started??     Previously this was not a potential solution because the VST adapter had issues with mono tracks, but with Superior 2 Drummer they are all stereo, so if I was able to get around the hang problem that way, it might be a viable workaround to live with.  And if Sonar still hangs then I will have at least eliminated another major possible culprit (Directixer).
 
Sonic
 

SonicExplorer
Going to a newer OS is not the answer, in 2 or 3 years the same paradigm will just repeat itself and there will be people saying to upgrade again.  There's absolutely nothing conceptually wrong with an W2K/XP box and slew of software designed to run on it. All of which I already know well and own, along with all the compatible hardware and drivers. Which I can keep running and servicing for many, many years to come.   There's just one maddening intermittent quirk hiding someplace in this new DAW that needs to be figured out.

 
I totally understand and respect that attitude. I was thinking more along the lines of being able to get support from here for example, not many peoeple run XP anymore and will not know all that much about it. W2k, hell, not many people are ALIVE that knows about that one! just kidding :)
 
I hope you figure out what the problem is!