Hmmm. Maybe someone else will be able to provide better insight, but it sounds to me like it could be a couple things.
First thing that will almost definately fix the problems:
CMOS Battery Failure to me means the the litium battery on the motherboard is bad. This same conclusion is supported by the Checksum error, as well as the time not set error. This is a battery that can be replace at wall mart. It's simply a watch battery, you just need to find the particular size that yours is, you can either record the size(should be printed on the top of the battery)
or you can take the battery out and take it with you to the store. I would start there and if that doesn't solve the problem, you may want to check your motherboard itself. Try updating the BIOS, or if you didn't build the machine, call the vendor and ask for a replacement(if it's under warranty). Let us know what happens.
EDIT: > woot, 100 posts!!