Problem with the motherboard

Hi guys, I bought a new PC before 3 months ago with these specifications:-

Intel Core2Duo E6750
Asus Commando motherboard
2GB RAM DDR2
120 HD + 300 HD SATA
Nvidia geforce 8600 GTS
Windows Vista Home Premium 32bit

I build the pc and I flash update the BIOS to support the 1333fsb, installed the OS and everything was working fine.

The problem is that I after a month or two I start up the PC and I found this massage at the bottom before starting windows.

"CMOS checksum Bad
Overclocking failed! Please enter setup to re-configure your System

Press F1 to Run the SETUP
Press F2 to load the default values and continue"

First I am not doing any over clocking
I press F2 to load the default values and the computer starts without any problems.. Yesterday it happened again, this time I tried to run the setup to check the BIOS configrations (everything was fine and far as can see) exit it without changing anything and it load windows without any problems. Today it happened again also , I dont know what to do any more. So please guys HELP.

And thank you in advance.

Note: Before posting this topic I made an update to the BIOS, in case that this problem may go away, but it is still the same.

system restore?

The only change that I made was updating the BIOS to support the 1333fsb
; usually this motherboard support only 1066 fsb but by update the BIOS it will support the 1333fsb.

I didnt do any overclocking or anything.

I try to see what I can do with the CMOS, can any one give me more information about it?

Try the battery. You haven't used it in a while, some batteries will die if not charged for a lengthy while. Had similar issue with socket A 2000+ Athlon, battery wouldn't charge and reset front side bus speed to default 100MHz instead of 133MHz and gave an OC BIOS Chk sum error. To find out if you have a similar problem go to control panel and select system properties and see what speed windows assigns to your processor. If it's odd, in the case above it said 1200MHz and should have read 2000+, then check what the proper FSB of your processor should be and reset it in the BIOS. If the system boots error free, as it won't lose the info while the system is on, then you will need a new battery for your main board. Take it to a PC shop and ask them to change it for you. Any more than $50.00 bucks find someone else. You don't need to panic about this behaviour as this is a safety issue and generally termed a "fail safe boot," the message is simply to alert you to the fact that the CPU is nor recognised by the system so is booting at a lowest default speed to prevent potential damage to the system.