That sucks, I hope you backed-up everything (assuming you were doing an upgrade) I would wipe the drive and do a fresh install to see what happens. What version were you running before you did this? What type of machine do you use? Do you have any un-common hardware?
During the fresh install disconnect all hardware (printer, scanner, camera, usb devices, everything) except the bare essentials (mouse, keyboard, and monitor). If you have any SCSI Cards, or any other types of cards pull them out until the install is complete. See if this works.
