ASUS K8V-SE & new 8800gt no post

I have just bought an 8800gt xfx as my old 6600gt died. But the trouble is, the system won't post or boot with this new card in. I should probably point out that the old card was AGP and the new card is PCI-E. Does any one have a similar set up or have any idea why this may not be working?

http://www.asus.com/products.aspx? [...] odelmenu=2

And this is a surprise for you? You have a motherboard that accepts AGP cards, and wonder why PCIe cards won't work on it? You bought the wrong card, it wont' work in your motherboard. Either buy a new motherboard that supports PCIe video cards, or send that back and buy an AGP video card.