Thanks for replying.
I have already cleaned my RAM and changed its slot. But that does not work. I have also used memtest86+ application in which it says no errors until ten pass. (It took about three hours to complete the ten pass and after that I cancelled it).
Since I get the blue screen when the setup says 'trying to detect the previous versions of windows .........." I guess that my problem is with my hard disk. Does the memtest86+ application test hard disk as well?? If so, how do I select the hard disk (it does not say what it is testing) and if not is there any other applications that test hard disk? (May I remind that I cannot boot my computer at all)