Computer freezing/Game framerate problems

[Hoverbear]

I have a custom computer with a 3.40 GHz processor, 2.75 GB of RAM, and a GeForce 8600 Graphics card (I can provide more info if needed). For some reason when I play games (League of Legends mainly) I will run okay for a game or two, and then all of a sudden in the middle of a game my framerate will drop from 60-30, down to 3-10. Also I can't leave my computer running and walk away because after awhile the whole computer will freeze and the only thing i can do is to do a hard restart. My old computer died on me and this was my spare due to the fact that I really can;t afford a new one at the moment and this lag in-game makes it pretty much unplayable, and since i cant leave my computer running it's pretty much impossible to download any large file, so if I could receive some possible help on this situation I would greatly appreciate it. Thanks

[Crafty]

Freezing could be a number of things, like overheating, virus, spyware etc. Make sure the computer is not overheating first - Check Cpu temps and clean any dust out of the computer. I would then get a spyware program and check for spyware, I use super anti spyware free addition for my spyware checks, but there are other free ones about. Also, scan for viruses, if you haven't got an Anti Virus program installed then get the free AVG one.

[Hoverbear]

I have an anti-spyware/virus protection software thats not the problem. I checked for malware, and i checked for overheating. None of these are the problem. if it was an easy fix like those I wouldn't be asking for help.

[Crafty]

Well how about you say what you have tried and then we will know not to mention it? I was going to say maybe your Graphics card is overheating but have you already looked at that?

[Crafty]

List below of things that could cause computer to freeze if faulty, so I would suggest testing these with diagnostic software.

RAM
Hard Drive
Virus, Spyware
Windows, Corrupted
Overheating