@Clive
I think the time has come when you need to seek professional help with this problem, if the computer is crashing,, freezing showing unpredictable behavior like this there is something defiantly wrong, If I were you I would save all your data format the drive and reinstall XP or another OS if that doesn't work take the computer to a repair shop and let them look at it, a computer that is not reliable is worse than no computer at all and at any time you could loose all your program data and files
Brian :'(.