Game-play very slow in 7600GT after playing for a while.?

I'd say it could be a number of things:

1) Defragment your hard drive - maybe it's not the video card

2) Video Card is overheating - download HWMonitor and see your GPU temperature. Add case fans to help with problem.

3) CPU is overheating - download HWMonitor. Your heat sink fan may not be working properly/ be adequate and your CPU is overheating. You may need to replace it. An additional case fan may also help with this problem.

4) Video Card needs latest drivers - go to the maker's website and download the most up to date drivers.

5) Power supply inadequate - your power supply may not produce enough watts to power your system, or it could be failing. Find the output wattage of the PSU (it is a sticker on the unit), if your graphics card exceeds this rating, you may be

6) Your video card may be failing on you - See what the warranty on the card is, and maybe you can send it in to get fixed. If your warranty has expired, you may need to buy a new card.

Run HWMonitor, then run your game with HWMonitor in the background. When you start to notice some slow gameplay, quit the game and look at the CPU/GPU temperature maximums.

CPU 55-60^C and up = HOT

GPU 60^C and up = HOT

(These temperature limits are usually listed by the manufacturer and you may wish to look them up as these are general temperature figures.)