My only suggestions would be to try System Restore from Safe Mode if it will allow you to boot into that mode by tapping F8 repeatedly while booting up or restore the machine to factory settings, using whatever recovery options are listed in the literature that came with your machine. Or you could try Technical Support to see if they have some ideas. They are better qualified than we are when this sort of thing happens. It's free by phone or online chat and is linked under Useful Links at the top of this page.
Insert windows 8 installation disc and start the computer.
Choose to boot using CD/DVD.
Now in the Windows 8 screen, click next button.
Click on Repair your computer.
Now select Troubleshoot.
Select Advanced Options.
Select StartUp repair
This will start diagnosing the issues and will repair the PC. Please revert back if you still face issues.