I had a fine install of Windows 7 alongside Snow Leopard.
I had a power outage, and Windows restarted. When I booted via the "Hold Option" sceen, it started hanging at the grayscale "Windows logo" (squares) that comes up after picking the Windows drive from the bootcamp loader (the Windows version of the grayscale Apple logo when OS X loads).
I think this happened once before, and installing rEFIt helped. I did that, but it continued to hang at the same point.
I finally got fed up with it and erased the Windows partition via Disk Utility. I then reinstalled Windows 7 x64 from DVD to the fresh partition.
Seemed fine. Ran Windows Update then restarted. FFFFFFFFF. Hangs in the same place.
What can I do? Like I said, I already have rEFIt installed. Booting the Windows 7 install CD results in the same infinite loading error. I don't have a spare Snow Leopard disk handy.