Hmm....odd. Do you get anything at all? No BIOS etc?
Have you tried booting in safe mode at all? I say this, because sometimes graphics cards will default to a refresh rate too high for a monitor to handle, especially older monitors. I mean, mine is only 3 years old, but can't handle 85Hz, only up to 75Hz. So, starting in safe mode will only load basic graphics drivers, and set the refresh rate quite low.....especially as you are booting from a pre-loaded XP...which will probably need a repair BTW, at the very least. Also, it will need the mobo chipset drivers installed for the new motherboard...which could also stop the vid card working I guess...but it should still work as a basic card...otherwise you wouldn't be able to install anything..lol
If it's not that, then remove and reseat the Graphics card. Might just need that.
Scorp.