My system keeps freezing, crashing, etc.

Alright so my computer is constantly freezing for about a minute at the very least, sometimes I have to restart, task manager is telling me that firefox is currently averaging around 100, 000 - 110, 000k. Seems quite not right if you ask me.

Msn also seems to be using a fairly large amount.

I was wondering if this is the problem but I'm not sure.
Last night I performed a harddisk check and scan because windows seemed to think there was a problem with it, not sure what the results were because I left it for the 3 hours that it took and came back as it was finishing. I tried a system restore, didn't fix it.

I have no idea what to do, any ideas?
Sorry if this is the wrong section, I figured this is the only place it fitted.