I have the same motherboard and experienced a similar problem with a different video card. After fiddling with the bios etc. It turned out that the card wasn't seated all the way in the slot. I removed the card reinserted it and everything ran fine.
There is an Iwill motherboard forum at the following address:
http://www.amdmb.com/vb/index.php
Check it out, I was able to find out alot of answers.
Also Check out the online Faq at:
http://www.x-faqtor.com/KK266.htm
This was also extremely informative.
If you computer isn't booting at all, it could be some sort of hardware conflict. Try reseting the bios back to failsafe defaults.
Soran