My computer runs fine with 500K RAM. Up until about a fortnight ago, that wasn't the case, it was always maxing out, but then I had internet problems and accidentally rebooted windows and lost everything, but since then my computer has been running perfectly.

I'd suggest you either have a virus or it's full of pointless programmes running silently or causing a conflict of sorts.

Rebooting isn't a bad thing if you back your important files up (unlike me, I lost my database, music, photos, my football manager game save that had been going for years, and some quality porn).

This should be a last resort though.