I'm watching the cost of repair and if it's too high I'm replacing my PC. It's over 6 years old. Checking RAM 1st!
 

First, best of luck to you! This is always a very worrying and stressful situation.
 
Here's what I'd do immediately (and I've actually done it): Try to recall whatever you've done in Sonar that's meant something special to you and copy it somewhere, even if it's not in its most desirable form - Just get your most valuable material copied somewhere safe, somehow, before you do anything else. If your computer goes irretrievably belly-up five seconds after you've managed to do this, you will eventually bless this advice. 
 
After that's done, you can go for completion. Others on this forum will advise you much better than I can in this regard.
 
But make sure you have that very special material copied using whichever way is quickest and easiest before you set out to make sure everything is done properly.
 
That's my advice and it may be silly, but it's free :)
 

promidi
If you do a full complete backup of your entire hard drive(s) (including OS) to a separate external drive using a proper backup program, you should not lose anything.

This is something you should be doing on a production machine anyway on a daily basis.  I do the OS backup once a week and a work files and settings backup nightly using a scheduled backup solution to an external drive.

If your repair shop just changes the motherboard/cpu and ram, the data on your existing hard drive(s) should remain intact.  Once you have reinstalled your OS to how it was before, then you can restore your user data from backup

Once thing I would do is take note of your drive partitioning information and drive letters of all drives - you will want these replicated on your new machine - especially if you decide to change the whole lot to a brand new machine.

that says it all - disk backup mandatory at regular intervals

RehabRob

promidi
If you do a full complete backup of your entire hard drive(s) (including OS) to a separate external drive using a proper backup program, you should not lose anything.

This is something you should be doing on a production machine anyway on a daily basis.  I do the OS backup once a week and a work files and settings backup nightly using a scheduled backup solution to an external drive.

If your repair shop just changes the motherboard/cpu and ram, the data on your existing hard drive(s) should remain intact.  Once you have reinstalled your OS to how it was before, then you can restore your user data from backup

Once thing I would do is take note of your drive partitioning information and drive letters of all drives - you will want these replicated on your new machine - especially if you decide to change the whole lot to a brand new machine.

that says it all - disk backup mandatory at regular intervals

 
There's some room to argue for file based backup....
 
Sometimes, it's just easier to simply start anew and simply copy the backed up data files over. This is especially attractive option if you're considering replacing aging hardware, since the OS is going to come pre-installed and is newer, and sticking with the old OS doesn't make sense.

You won't be able to copy the OS from one computer to another, because each PC's motherboard chips/devices are going to be different, and the drivers for one set of those won'r work for a different set you would get with anything but an exact match for motherboard and revision.  In addition, the programs would all have to be installed anew on the new load of the OS on a different machine as well.
 
Consequently, I never worry about backing up the OS, other than a single time for recovery to the same computer, should the primary hard drive fail, or some other need like that - corrupted Windows, ransom ware, etc...
 
I bought myself a 6 TB USB 3 external drive to back up all my non-OS data, such as projects and user documents/pictures/videos/etc.  What I do NOT do is keep backing up old static projects or user data.  It is all backed up once, and then I periodically backup new or altered projects and user data, that has changed or is new since the full backup.
 
Additionally, for ME, I already have an external drive that my Komplete 8 Ultimate samples all came on, so I don't bother backing those libraries up again.  I have another 1 TB in sample libraries from downloading the complete Composer Cloud collection, and I DO have those backed up once, but again do not need to keep backing those up as they are not only stable, I could always download them again.
 
So, with some thought and organization and consistency, you can (and I recommend you do), back up things that are new/changing, on an ongoing basis, without having to devote massive amounts of time to do so, and for user data that is static, you can do quite fine with a single external backup of those data.
 
Even with a brand new backup drive, it only has a 3 year warranty, and some only have a 1 year warranty, so keep that in mind - investing in a new backup drive for less than $200 every couple of years is well worth it to ME, just to be safe, which is the whole point.  That is FAR less money than it would take to somehow try to recreate projects - particularly those with audio tracks.
 
Internal hard drives also have dwindling life expectancy anymore.  Seagate used to offer 5-year warranties, and now often only offer a 1-year.  Western Digital has some that are 3-year and some that are 5-year, and refurbished drives typically have only a 90-day warranty.  I had a couple of SSD's crap out in less than 6 months, though that was a couple years back, but I still am not sure of their longevity, so I backup backup backup.
 
Bob Bone
 

SuperG
I'm having problems with my PC and am afraid It may need to be replaced. If this happens how do I reinstate Sonar Platinum, Melodyne Editor, and Addictive Drums on the new PC? What will I lose?

The licensing for Melodyne and Addictive Drums are handled independently by Celemony and XLN.  Both of them limit you to two simultaneously activated PCs.  If you find that you've used up your licenses already when you activate the new PC, you can go to their web sites, log into your account, and delete the activations for the old PC to free up those licenses.  I'd suggest doing this even if you still have the extra licenses available since it'll open them up for your use in the future.

What I do is never store data on my OS drive. My data is on a second and third drive. So a new computer is as simple as swapping those drives to the new machine.  
 
Those drives are also backed up to external drives and most of my files are in 4 places or even more.
 
That Dell will still run for a long time yet as long as nothing fries the MoBo.
Parts are cheap. I still have desktops from P4 days that run smoothly.
An i7 quad seems more than adequate to me. Upgrade the RAM to 16 Gigs.
Add a SSD as your OS drive and away you go.
 
Or buy a new one but keep that as a back up or use it for office and web browsing.

Thanks guys! I pulled the panel and reinserted the RAM chips then cleaned the interior. I checked all the connections and as you can see, here I am! I ran a systems check and no problems were noted. It seems to be running fine now. 
 
I lost most of my project work in 10' after my divorce and started anew with this PC. If I replaced it I will start anew again but this time do as Cactus suggest and use this one for browsing!
 
Thanks for all the input!