My PC switched off the other day by itself and now I get no post, no beeps. Its and Asus P5B and I've tried different CPU and PSU on it. Drives spin up and onboard motherboard power LED on but no chassis power LED. Just the HDD LED permanently lit. Optical drives do not eject :/ It doesn't even beep when no RAM installed. CPU does not get warm, even without heatsink on.
It could be anything from a short, bad capacitor, or corrupt bios. Whatever the problem is its preventing the bios from communicating with and initializing the system devices. It might be time for a new board. Try this, remove all the memory sticks and clear RTC ram, add one stick to the B1 slot and see if it will post. Might want to try another CMOS battery as well if you have one although there should have been signs the battery was failing. Too much dust inside the case could be another factor but it might be to late to clean it, blow it out anyways if it hasn't been cleaned in a while. Clear RTC RAM (3-pin CLRTC): 1. Turn OFF the computer and unplug the power cord. 2. Remove the CMOS battery. 3. Move the jumper cap from pins 1-2 (default) to pins 2-3. Keep the cap on pins 2-3 for about 5~10 seconds, then move the cap back to pins 1-2. 4. Reinstall the CMOS battery. 5. Plug the power cord and turn ON the computer. I seriously doubt a CrashFree bios recovery will work but if the above doesn't do any good you have nothing to loose. Download the P5B user manual from the ASUS site and see: 4.1.4 ASUS CrashFree BIOS 3 utility