|If nothing shows on the monitor correctly then it's probably the video card. But did anything happen to the pc between the last time it worked OK and the first time it didn't?|
If the PC also has an on-board graphics port, try the monitor there.
As for the card itself, with the power cord removed, pull the card out and reinstall it, making sure it's completely in the slot. Try booting again. If you get the same results, do you have another video card you can temporarily swap in?