I had this kind of thing on one computer a friend brought to me for helping.
Win7 crash after boot from Hard disk.
cannot boot from USB
cannot boot from DVD.!!
so what I did was:
unplug the cables to Hard disk and cables to DVD.
plug in a known working , bootable USB flash drive with Linux OS
it booted up and so it is OK.
Then I power down computer
add back the DVD cables
boot again, this time it can boot from DVD
so I power down and put back hard disk cable
now it still can boot from DVD and from USB
I run Live from USB, try to check hard disk, it was so corrupted that, at the end, I decided to reformat the whole hard disk, reinstall Win7 and since then it has been working quite well in Win7..
thought it might help you to try out. no guaranteed