BleepingComputer.com: CPU not diverting when running games

Hi, for the past couple months I have run into trouble while playing games. The two examples I'll use are World in Conflict and Civilization IV. When I run either of these games, they'll will run optimally for about a minute, but then will drop dramatically in performance (about 7fps), rendering them nearly unplayable.

I'll open task manager to find the processor running happily at 99% with computing not slowed down from the open game (since I have a single core, intel pentium4 this is usually affected). In addition nothing seems to be sapping processor power, it just seems to be unused. I have recently reformatted on a clean harddrive but this has not resolved the problem so I'm really not quite sure what's going on. I'm fairly certain this has nothing to do with video settings or things of that nature since these games have worked fine in the past. Any suggestions will be greatly appreciated!!

system info:

Manufacturer:
GBT___
Processor:
Intel® Pentium® 4 CPU 2.80GHz (2 CPUs)
Memory:
2048MB RAM
Hard Drive:
250 GB
Video Card:
NVIDIA GeForce 7300 GT
Monitor:
Default Monitor
Sound Card:
SB Live! Audio [A000]
Speakers/Headphones:
Logitech
Keyboard:
USB Root Hub
Mouse:
USB Root Hub
Operating System:
Windows XP Professional (5.1, Build 2600) Service Pack 2 (2600.xpsp_sp2_rtm.040803-2158)

video card .. overheating(fans working?), failure, drivers ? try another vid card to test.