Try restarting it again?
Use windows recovery from DVD?
You could always remove the hard drive and add it to the other system and copy off the contents you want then reinstall to that hardrive in the same machine fresh. Then put back on the content.
Hard way to do it- but it's what I would do as it is certain to work 100% perfectly. Fresh installs are nice sometimes.
"Too much is almost enough. Anything in life worth doing is worth overdoing. Moderation is for cowards."