Parallels stopped working

I have Parallels Desktop installed w/Windows 7 on my newish iMac 27" intel i7.

Firing up Windows and running PC-only applications worked fine for several months. Just yesterday I fired it up for the first time in over a month, and although Parallels itself seemed to start OK, and Windows allowed me to log in, te Windows desktop seemed to be having trouble opening on my screen in any view mode (coherence, crystal) and all the applications won't run...they crash instantly on start up.

Windows did install the 18 needed upgrades on start up, so the Windows machine itself should be current

Any help would be appreciated

R.