I'm stuck at "Windows is starting up..."

I had to Force Quit Windows because it was stuck. I turned my iMac off, back on, and Windows doesn't launch anymore. It is stuck at the initial screen "Windows is starting up..." right before the screen where I'm supposed to input my password.

Do I have to Unistall Parallels and reinstall it?

Thanks.

 

In your case, reinstallation of Parallels would not do any good since this is a Windows-related problem.
I would suggest to try loading the Last good configuration (presing F8 during VM boot to get the menu of startup options) or booting into Safe mode and try to use the system restore: http://support.microsoft.com/kb/306084
If there would be any troubles with it, I would suggest to create a ticket in our support line since a closer investigation might be needed.