I think that I might know what's causing this. When you switched video cards for the first time, did you use any kind of cleanup utility after you uninstalled the Nvidia drivers and before you installed the AMD/ATI drivers? If not, you're going to have to do this, because the drivers from both brands leave behind garbage files and registry keys that can seriously bork the installation of the other brand's drivers and cause the hardware interrupts that you're experiencing, along with BSODs and other nasty stuff. Here's what you need to do:
1) Download and install Driver Sweeper
. If the installation packages contain adware, be careful not to install it as well.
2) Go to Start>Control Panel>Programs>Uninstall a program and uninstall whichever drivers that you're using right now, along with all of the other stuff that has anything to do with them, then reboot.
3) Boot into Safe Mode (tap F8 at POST screen when the computer first powers up), login as an administrator and run Driver Sweeper. Clean for BOTH Nvidia and AMD/ATI display drivers. When it's done it will prompt you to reboot, but shutdown instead and install whichever video card you're going to be using (I assume that it's the 6950). Then power up and boot into Normal Mode.
4) Run CCleaner's registry cleaner. It will prompt you to back up your registry first, and I would do so, then fix any issues and reboot into Normal Mode again.
5) Now you can install the new drivers.
If you're still experiencing interrupts after all of that, then I would have to go with nuking it from orbit by reinstalling Windows. Last resort for sure, but we both know that will work if nothing else will.
On a side note: Tea Timer used to seriously kick my old Pentium 4's butt to the point where I had to disable it, but it should present no problem for any modern multi-core CPU like your hexacore.
"They should rename the team to the Washington Government Sucks. Put Obama on the helmet. Line the entire walls of the stadium with the actual text of the ACA.
Fix their home team score on the board to the debt clock, they can win every game 17,000,000,000,000 to 24. Losing team gets taxed by the IRS 100%, then droned."