there's no reason to upgrade or overclock the cpu, nor is there any reason to use "modified" drivers. the 1900XT should run just fine with std. drivers and a 3200+ (very few games, if any, or cpu bottlenecked after around 2.4ghz on an a64).
there's obviously some driver corruption, a hardware conflict, faulty piece of hardware, or some rogue apps taking away cpu cycles/memory...
the best way to troubleshoot would be to remove any and all unecessary peripehrals - extra hard drives, optical drives, sound cards, 5 of the fans if you're running 8
make sure everything is installed properly (for example if dual channel ram, have the installed in the right banks, etc.). unplug everything you can to leave as little load as possible on your psu (better to test with a known good one tho). if you don't have a psu with a dedicated plug for the vid card, make sure you don't have the adapter plugged into one that's on the same chain as hard drives, cdrom, etc.
run tests.
if it runs well, install a peripheral and check again, and so on and so forth until you find the problem.
there's obviously some driver corruption, a hardware conflict, faulty piece of hardware, or some rogue apps taking away cpu cycles/memory...
the best way to troubleshoot would be to remove any and all unecessary peripehrals - extra hard drives, optical drives, sound cards, 5 of the fans if you're running 8
run tests.
if it runs well, install a peripheral and check again, and so on and so forth until you find the problem.