PC won't boot up with new Graphics Card...

Any help with this one would be very gratefully received:

I have just installed a new Graphics card and Motherboard in my PC:

GeForce 5600 and Gigabyte GA-7VA.

The trouble is, nothing (nothing!) is displayed on the monitor unless
I remove the graphics card and refit it just before I switch the
machine on. If I leave the machine off overnight - in the morning the
graphics card has to be removed and refitted before it will boot up.
The harddrive and power light come on but there is no video.


I have cleared the CMOS and loaded the fail-safe defaults but I am
beat with this one...

....does anyone have any ideas?

Thanks,

Jo