if what TiSwAs said does not work (which it very well may) try looking in your mobo manual for the way to clear the CMOS - there should be a jumper somewhere on the motherboard to do that..just follow the instructions in the manual.
If there happens to be no jumpers or its too complicated, try removing the CMOS battery from the motherboard for say...15 minutes, and putting it back in..
I had a problem very similar to yours(that this fixed) where it was obviously getting good power, but for some reason it was just not even starting the POST and giving a total blank (orange led) on the monitor. How exactly the bios would get messed up, im not sure.. but its a very good possibility.
Hopefully that will help ya.
