It is hard to know what else to suggest without the term new motherboard coming to mind.
You can try this procedure, if you wish? It was copied from a now defunct web site.
"How to reset CMOS
Let's say that you've entered an incorrect BIOS setting and your system won't load as a result. Most of the time, resetting the BIOS back to its default configuration will cure the problem. The settings are stored in a piece of memory on the motherboard called the CMOS. By changing the "clear CMOS" jumper on the motherboard, the problem will be solved as it restores the BIOS back to a default state that will allow your computer to boot.
Somewhere on the board close to the bios battery (round and silver, looks like a watch battery) are a bank of 3 pins with a jumper on 2 of them. This is the CMOS jumper.
REMEMBER: Turn the power off from your system before resetting CMOS. Pull your power cable out of the power supply and wait for 30 seconds for residual static to discharge.
Whichever pins they are on, they are pins 1 and 2 with 2 always being the centre pin. To reset CMOS, take the jumper off pins 1 + 2 and place it on pins 2 + 3. Leave for 5 seconds and replace the jumper back on to where it was. The system will now boot up again but don't forget that all the BIOS settings will have been reset - including the date and time!
Enter BIOS by pressing delete or F2 (depends on your BIOS) and reset all the settings, apart from the one that caused it not to boot obviously.
You should always consult the motherboard manual when resetting the BIOS - just to make sure that you are changing the correct jumper."