First off, I'll get the specs out of the way:
AMD Athlon 64 X2 6000 3.1GHz Socket AM2 89W Dual-Core Processor
ASUS M2N-MX SE Plus AM2+/AM2 NVIDIA GeForce 6100 Micro ATX AMD Motherboard
Transcend 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model JM4GDDR2-8K
DIAMOND 3650PE1GOC Radeon HD 3650 1GB 128-bit GDDR2 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card
Thermaltake TR2 W0070RUC 430W ATX12V Power Supply
Microsoft Windows Vista Home Premium SP1 64-bit for System Builders - OEMSo here's the deal.....
My system runs everything fine, except for when I do anything 3D. Well, I take that back. EVERYTHING runs fine, including 3D, until I begin any kind of input (mouse/keyboard, gamepad, etc).
For example, I ran the Street Fighter IV benchmark and it ran perfect. It never gave me a single slowdown or anything. This morning I installed the game and it ran fine at first, but once I started playing, I began to get off and on slowdown. It was never related to anything happening on-screen. It just happened on a regular cycle.
This regular cycle slowdown has been the problem in everything. Games will run perfect, then slow. It's cyclical.
I bought Ghostbusters and everything ran great until they finally gave me control of my character. Once I was able to start playing, the slowdowns began.
This is the case with Far Cry, Far Cry 2, Left 4 Dead, GTAIV, Plasma Pong.....even Postal 2. Older games are even giving me this problem. I can set games to their absolute lowest settings and I still get this slowdown.
This problem existed for me in Windows XP SP2, so I thought if I upgraded to Vista 64, maybe that would help, but it didn't. When I installed Vista, it was a fresh install onto a formated drive and before I did anything else, I tried Far Cry 2 and the problem still existed.
So is this input related? I'm really stumped here and I've tried a lot of things to figure it out.
I'm not at home at the moment, so I can't try any suggestions right now, but I'm open to hearing any ideas on this. I've got a good gaming rig, short of being able to actually game on it!

Any help is appreciated. Thanks.