Bad checksum is almost certainly refering to an error in the CMOS data (the CMOS is the chip where your BIOS stores its settings).
Try "Reset BIOS to defaul options" or whatever the equivilant is, and save it. It may be as simple as that.
If that doesn't work you may have to blank the CMOS - there's probably a jumper on the motherboard somewhere. If you're lucky it'll be labled (BIOS_RSET or something). If you're unlucky it'll just have a number and you'll need the motherboard documentation to find it.
If THAT doesn't work, the CMOS is probably fked - in which case, your computer is going nowhere.
Incidentally, you didn't turn it on as soon as you got it in the door did you? You can get condensation on components after transport from the temperature changes - its always a good idea to give it an hour or so to clear up.
