COMPUTER HANGS AT ANY TIME

Hi, I got Celeron 1.1 processor, 810ET motherboard, 128 MB RAM pc. It hangs at any time whenever it wants. I have tried formatting whole hard disk even then it hung. I installed fresh Win-XP SP2 in it, immediately after that my PC hung. Even when there is just 1 Word file is opened it hangs. Sometimes it does not hang even after opening 7 files.
It crap! I dont understand y is it happening.
Please help me out it this.