My grampa's Toshiba lappy has a similar problem, though it's like 4 years old... it would constantly freeze, some programs would run dead slow, and sometimes stuff just crashed. I reinstalled, but that didn't do anything... however, when I removed the battery, it started working just fine. Pop it back in - slowdowns, freezes, crashes, etc.
I have no idea how to fix it, though, except for simply running the computer w/o the battery.