I have recently had a similar issue with Windows 7 on Parallels Desktop 7. If I have Office 2010 open, sometimes when Windows turned the display off, when I tried to wake it, I'd see the spinning wheel (OS X's, not Windows'). I noticed that there was a recent update to Parallels 7, and I also noticed that in the process of migrating my Boot Camp partition to my 2012 (using Winclone) I had forgotten to update my RAM and CPU allocation, so perhaps that had something to do with it. I'm experimenting with it a bit more.