Sometime when I turned my pc on, there is a message in DOS just before windows is being loaded. The message says 'CMOS checksum error - defaults loaded'. 'Press F1 to continue, Del to enter setup/dual bios/q-flash, F9 for Xpress Recovery.' How do I solve this problem?

Hya Shibly.

Maybe the motherboards battery needs to be replaced. How old is the pc?

Hi Shibly!
I'm pretty sure Joe is right, but what happens when you press F1?
Does your computer boot then?
Bluefish

Hi, thanks for the reply. When I press F1, my windows are able to start up. I am just curious why the message appear though. My PC is DIY and my motherboard is about 2 - 3 years old. How do I change my motherboard batteries though?

Well you could first try to reset your BIOS.
Make sure the PC is not connected to the wall socket.
Open the case, and you'll see round flat battery.
Close to that, there will probably be three pins, with a jumper on 2 of them.
Like this:
[ . . ] .

Set the jumper this way:
. [ . . ]

On the other 2 pins.
Hold it there for a minute.
Then place the jumper back, reconnect your PC and start it up.

If you're not sure what to do please post back.

Bluefish