Ever since January, as soon as my computer heats up, it starts to run slower on some things. After I turn on my computer, I have about 20 minutes to do whatever I want before it starts to get warm. As soon as it gets warm, certain things don't work. I play an online full screen game called Gunbound which uses 2-D graphics. After the 20 minutes are up and my computer is warm, Gunbound starts to run very slowly. Things affected by it include: High quality internet videos, DVD's, games, anything having to do with graphics. Things not affected internet surfing, load times, pretty much everything not having to do with graphics. Whenever I do something that causes my computer to run slow, my CPU usage jums too 100% and goes down when I stop. After a while, my computer gets too hot and turns off. Before January everything use to work, nothing got slowed by anything, I had no over heating problems, Gunbound would work at all times. I tried doing a full system recovery, then I reinstalled Windows updates, reinstalled all my anti-Spyware/ Virus programs, and I put some of my old files onto the computer. It still didn't help the problem. I even tried increasing the RAM.

Computer Specs:

Toshiba Satellite Notebook
Windows XP SP2
1 GB RAM
49.5 GB free of 72 GB (on hard disk)

per chance, is your processor an Intel Pentium 4? if so, the problem would be that the Pentium 4, when it starts to overheat, it clocks itself down, slowing down the processor. which would explain, that when it get hot, it slows down, and hte cpu usage jumps, because it cannot do as much work as it could before. It is likely that your computer fan either died, or it is clogged with dust.