Check your data cable to mother board and Hard disk. If the cable is loose kept then such problem occur.  I recommended you to check the data cable of harddisk and also tight the RAM.Sometimes the System Hangs up because of power supply also. So check it up .Again if the problem was not solved then its sure that there was missing some document  and your RAM was reading the temporary files.So to solve it your have to install window system once again. Thanks