Why wont my pc recognize an AGP x8 graphics card

Hello,

im running a very old emachines 770 model, had to put Vista business on it  

my friend recently found a very cheap 256 mb GeForce FX500 5500 graphics card and bought it for me... so i went to install as you do lol..

comp config:
pentium 4
768mb DDR Ram
AGP slot
Trigem imperial IM845G motherboard
350w PSU

i was wondering if this motherboard can actually handle this graphics card because i have tried to install it a few times..

uninstalled old drivers for the GeForce 4 MX 440 graphics card and then turned machine off put new card in turned on and nothing completely black screen... (i use a program which allows me to look at another comps screen and control it so i used that to go into the device manager to see if it had even recognized that i put a new card in the AGP slot and all it says is that its using the onboard crappy one...

any ideas???