Hi,
I think you are having a problem of Boot sector viruses.
Please check below links:
How to collect Master Boot Record for submission to Symantec Security Response
http://www.symantec.com/business/support/index?page=content&id=TECH93277
Boot-Sector Viruses
You may receive a "Stop 0x0000007B" error message if your computer is infected with a boot-sector virus. If the problem is intermittent and you can start Windows, check your computer for viruses. If you find a virus, also check any floppy disks for viruses before you use them again.
Also refer below microsoft article.
http://support.microsoft.com/kb/324103