Can Not Start any Guest in Linux Host

I am running Fedora 12 and have successfully installed Parallels. all the programs launch fine and I can create a virtual environment.

Trouble is, when I try to launch the virtual environment, I just get a black and blank console with the timer in the middle that goes round a few times. Sometimes the mouse may be respone for a few minutes before everything locks up requiring me to physically restart the computer.

That's with Windows and Linux guests. Everything seems to check out OK, so I don't know what's going on.

Any thoughts?

Cya
Simon