Random crackling and popping sounds when using USB Interface

So, I have been successfully using a Tascam US-2000 in Sonar for the past three years. I am currently using the latest version of Sonar X2a and record in 24-bit. Everything was fine until recently, I now have this random crackling and popping that is audible when monitoring with Input Echo and is present on any recorded tracks. I have also had a few occurrences where the computer just rebooted while I was watching a video from Groove3 as well as the "Blue Screen of Death" a couple times (also while watching video). I failed to capture the blue screen, but it mentioned something about USB_"something" (should have really written it down). I have owned this computer for maybe four years. It is a custom built tower that has an Intel Corei7 and 8GB of RAM. It has never let me down on performance latency, even when piling on plugins (well, there are limits but I could do a lot more than I can now and not get dropouts). It never used to restart or give me a blue screen. Something is going wrong now. The random crackling and popping, blue screen, restart, and also when I record anything and play it back, it is WAY off on the timing unless you save the project and restart Sonar, then it is in time but has the clicks and pops. Also, it is constantly dropping out, even when I crank the latency WAY up on a simple project that has very little hapenning. This is not Sonar's fault. I can also hear the same crackling and popping when I use IK_Multimedia's Amplitube BUT only with the Tascam US-2000. If I use the StealthPedal, I hear no pops or crackles. So, seems like the Tascam is crapping out, right? WRONG! I hooked it up to my laptop and ran Amplitube and NO PROBLEMS! I used a different cable to go from the Tascam to my laptop, so I used that same cable to run to my PC but that didn't help. I also tried some different USB ports with no luck. So, it is something wrong inside my PC or some kind of conflict maybe? I plan to open it up this evening and blow out all of the dust, then try hooking up the Tascam as the ONLY USB device to be plugged in and see what that produces. I have a backup image that I can go back to when I think that this problem was not happening but I want to try some other things first. Has anyone had an issue like this before? Any ideas that I haven't mentioned yet?

Make sure you're connected to a USB2 port.
Try swapping out the USB cable.

Also, check to make sure one of your HDs isn't currently running in PIO mode (which would kill performance).

A few things, Tascam drivers are noted to be not stellar, but you say all has been good so far? 
As always check the Tascam site for both firmware and driver updates first. There have been a few. 
Think about any changes you might have made to your computer and updates. 
Sometimes things you optimized before flip back to defaults after windows updates. 
But crackles are commonly caused by your system crapping out on you and driver issues. Try by passing all efxs bins while recording, I have to do this if certain plugs are being used.  

My computer automatically downloads windows updates, so that certainly could have something to do with it. I do have the IK_Multimedia "Stealth Pedal" which you can consider to be an audio interface. When I run Amplitube with the Stealth Pedal, I don't hear any popping or crackling. I used it without removing the Tascam. I don't have any other audio interfaces to try. I am using the latest drivers for the Tascam but reloaded them anyway. I didn't try removing the drivers first, though, so I might try that after I clean the box tonight. I am normally pretty good at troubleshooting but it's hard to know when this started really happening. I know that it was not a problem on my last bit of recording sessions as they play back pristine. They are over a year old, though! A lot has happened since then as far as updates, new software, etc. I can live with a total re-image back to factory, if worse comes to worse. My last backup that I made (system image) was over three months ago, so I would start with that one first. I am just praying that it isn't some hardware going bad inside the box, like motherboard or RAM (well, RAM would be better than motherboard, huh?) Thanks to everyone for the tips so far. I should know some more in the morning after I devote some time to it and will be sure to post results whether it is fixed or not. Keep the suggestions coming though, because I am stuck at work and freaking out about it.

Well, last night I tried a bunch of stuff. Firstly, I took the covers off of the tower and blew all the dust and cat hair out of the PC. It was a bit dusty but I have seen much worse. I then plugged in the Tascam US-2000 ONLY and fired it up. The sound was even WORSE! Now the popping and crackling has turned into REALLY garbled sounds on EVERYTHING!! Just the regular Windows sounds or trying to play an MP3 results in squealch and jibberish. I rechecked the Tascam on my laptop and it works like a dream (same USB cable) so I know that it is not the Tascam. My daughter informed me that she had been getting more Blue Screens and reboots, so it has gotten progressively worse over the past month. I started unloading updates and drivers to no avail. I then just got fed up and re-ghosted back to a system image that I created in January. At first, I thought that it did the trick. I started to play a song in Media Player and it just sounded terrible. Any sounds are now degraded. I'm really starting to think that the Motherboard is having some issues. Since I re-ghosted the system, I was unable to look at the Event Viewer (should have done that first). I do remember that what I saw on the Blue Screen said something about USB, which would make sense because this is a USB interface but I don't know what to try next. I tried it in EVERY USB port and it sounds terrible in all of them. I know for a fact that it didn't sound like that in January when I made the image, so I don't think that re-installing Windows from scratch is going to help, do you? It really seems like something hardware to me but I am asking for input.

if your computer has a wireless connection disconnect it.
go to device manager,select your network wireless driver.
right click and choose DISABLE
this is totaly reversable,just right click it again and choose ENABLE.

wireless cards are big killers when it comes to picking up interference.
wireless intereference signals.

if this isnt the case and it doesnt cure your cold.
then retrace your steps and use logic,was it something i did by going to 24 bit,when did this happen,what did i change?
more importantly,what could sonar have changed to use as a defualt ?

its all common bro.

Okay, good news and bad news. My guy was and I were correct: The USB Controller Chip on the Motherboard is baked, either from overheating or from a surge. Either way, I can't use those USB inputs any more and I may need to buy a new Motherboard. I asked him if he thought I could still have performance issues if I did not have anything plugged into the USB inputs for the Motherboard but only used separate cards. He said that it would be impossible to know without just trying it. The card from work only has 2 USB inputs (which isn't near enough) so I would need to purchase at least one more 4 input card. So, for anyone that is having similar issues, you can try what I did. I will continue to do some testing with the one USB card and see if I have any performance issues. I will post back if anything happens, otherwise it's working fine.