No video after powering down pc

Hello,

I have a compaq 6470nx that has no video display after power to the pc is shut off. The video is fine if I do a restart, but if I do shut down, it takes several attempts at restarting the pc before the video will go. I've tried replacing the video card, went from agp to pci, replaced monitor, cables, etc. I've had no other video issues and I'm thinking its just the MB that is going. Any other ideas?