I received a laptop the other day that was horked beyond belief. I was only able to run the anti-virus once before the machine died. And try as I might, I was unable to boot the machine back up. Using a linux live-CD, I was able to verify that the drive was physically good and in working order, no bad blocks or sectors. However, upon booting, the BIOS screen displayed, then nothing. Blackness. If I tried safe-mode, I could see a bunch of dlls loading, but the machine continually hung on on dll.
I went to a faithful standby, Trinity Rescue Kit. I ran all of the tools (that were appropriate,) and still nothing. Most of the errors seemed to be "illegal access" errors, or logic not supported.
Finally, I decided to use an old version of the registry. I followed the directions on this Microsoft page, and BINGO. I was able to reboot the machine. Fortunately, I copied the Documents and Settings folder of the user. So, I was able to put the files back.
Some software will probably have to be re-installed. And the machine is not the most stable. But it is a real old XP (Media Center) laptop, and could probably stand to be updated to Windows 7.