Parallels Freezes on "Power On" of Guest OS ( Has worked before, Ubuntu as Host OS )

Hello,

I had Parallels running for two weeks now. I had some troubles installing on Ubuntu Linux 7.04, but after reading this Forum and exchanging the "prlnet.c" as suggested by this Supportforum everything worked fine. ( Beforehand parallels-config would throw errors on compilation of the drivers ).

Now this morning I urgently needed to start my Guest OS Windows XP Pro, but Parallels would not start up. It said that it was installed but not configured and I should run parallels-config as root ! Well, so I did. The compilation was no problem and said I could now issue the "parallels" command.

NOW: Parallels is starting up, but when I "Power On" my Guest OS Parallels just Freezes !!!

Need Help ASAP !!!
( Intel P IV, 2 Gig Ram btw. )