The other day I upgraded my heat sink to the hyper 212 plus from an old stock CPU cooler. When I put everything back together, I couldn't get the system to post until I cleared the cmos. After I did that, I got an error having 2 gigs ram so I only put in one stick. Every time I shut down the computer I have to clear the cmos (LED stays blank on MB) before it will post again. When the computer does post, I get a corrupt cmos checksum error (loading defaults). I cannot change any settings in the bios.
Initial thoughts - Maybe I shorted something out with the big hex nuts on the CPU cooler. So I reinstalled the hex screws making sure it wasn't in contact with the circuits on the MB.
Next I thought maybe the battery on the MB was dead. I checked in the BIOs for +Vbat it said 3.06 volts.
I booted into windows 7. I don't think it's my power supply because everything else is working fine.
Operating System: Windows 7 Ultimate 32-bit (6.1,build 7600)
You should clear out the bios, here is how you do it. First remove power, then remove motherboard battery, then press power to remove any residual power. Plug everything back in and see if you can get a proper post.