you will need to isolate the fault either hardware or software, if you have a spare hard drive and install Windows xp, and test it, if it works then you will know it is hardware fault, check thermal paste on processor, if it is blackish on it, cleaned it and reapply thermal paste.
If it is software fault, you will need to re-install software.
http://www.pcglow.co.uk
Gareth Gunn, November 2007