Problem transferring XP from 3 to 4

I upgraded from 3 to 4.0.3810 on my iMac 2.8 GHz with 4GB Ram. Using OS 10.5.6. Seemed to work fine until I tried to bring in my Virtual machine... Windows XP. It seemed to finish and the XP machine shows in the Virtual Machine List, but the screen is absolutely black. Start, shut down, nothing works I see only a black screen. Of course I chose to convert to 4 not backup. sigh. Can anyone think of anything I can try or do I have to lose all my virtual machine and start over? Thanks