Re: Power supply?
An old or under-powered PSU will not cause a computer to physically slow down but rather cause unexpected power-downs when it can't supply appropriate power.
Most likely a RAM issue though. Check for RAM usage.
If you are using a 32-bit OS, a good chunk of your RAM will be used during installation and will not be available for use.
Have you heard any clicking noises coming from your hard drive lately? Oftentimes, a failing hard drive can dramatically slow down a computer...especially during intensive tasks like games.
XPEX Vortex 3620 Mid Tower, Rosewill 450 Watt PSU, MSI P6N SLI Platinum 650i, Intel Celeron D 356, 2GB G.SKILL DDR2 800, Western Digital 40GB, (2) EVGA 7950GT 256MB Video Cards in SLI, HP DVD Multi-Burner, Windows XP.