I think I've found your problem!!!
you have no PSU
seriously though, theres nothing wrong with this machine, I've got a board like that, (practically the same) but a slightly different version I imagine, still use it now, it sits in the corner acting as my general server running windows 2003 quite merrily to it's self!
as Setis said, you'll find a number, (it's just in between either two of the PCI slots, or APG (if it has them))...
the letters ate about a half inch high and the paint will be white...
post that here and maybe someone can help, (my first thoughts are that if it's like the one I have it may be set to use onboard video only!!
or maybe your graphics card is bust...
since you say it's not your main computer, you could try swapping the graphics cards with the one you have in your main machine?
you might want to bear in mind that if it's the same age or older than mine then it's limited to AGP2x (I think). certainly I have had problems with cards that I absolutly know work because I've tested them in other machines!