Ok, i brought a 9800GTX and have installed it in my computer but when i boot it up theres just a blank screen it doesn't even go to BIOS but all the little power lights go on. I Was using a 7300gs before and i tried putting that back in and it didn't work so i think I've completely fudged it up. Any ideas why it no worky?

my spec are:
500w omni PSU
AMD X2 4400+
3gig RAM
M2N-MX-SE motherboard
Got bored left. Got bored where I went away to. Came back.