|OK, assuming nothing works (you get absolutely no display?), about the only option at this point is to reset any BIOS options to the defaults.|
Here's the manual for the GA-81915G DUO motherboard.
The CLR_CMOS jumper is shown on page 26 of the manual. Instructions are to short the two pins. Apparently they do not include a "shunt" to do this so...
1. Unplug the power cable (cord) from the power supply.
2. Find a jumper (shunt) you can use or use a screwdriver etc. to connect the two pins.
3. While you have the two pins shorted, press the power button.
4. Remove the jumper (shunt) or whatever you used.
5. Plug the power cable (cord) back in.
6. Push the power button and see what happens.
7. Let us know if it worked or not.
The jumper *shunt) looks like this...
All they do is make a connection between two pins; just like a screwdriver blade, paper clip, or any other hunk of metal.