Did you leave the bios reset jumper cap in the reset postion? I had an Abit A8N Ultra where I left the bios jumper cap in the "reset" postion (forgot to put it back) and I had this same problem. Bad news for me, it killed the board. I've still got it in the vain hopes that somehow it will work again when I have the time to play with it. But Abit told me that it doesn't necessarily kill the board, so you might not be out of luck.
I will tell you what they told me (if memory serves). Check the Cmos battery with a multimeter or something. It should read 3.3v (I believe). If its OK, unplug the box and press the power button (to clear any remaining electricty in the thing). Then take the battery out for an hour (I think an hour is unecessary but that's what they told me). Put it back in and see if it boots with the default bios options.
If the jumper cap is not the issue, it could be simply that you set somehting inocrrectly.