The CMOS checksum error is commonly associated with failure of the coin cell battery on the motherboard. Given the systems age, this is also a possible reason for your problem (although usually batteries last a bit longer than 3 years - perhaps 5). You're best bet is downloading your motherboard manual from the board makers website (or possibly even on the CDROM that came with the motherboard) and following the instructions in there, change the battery for one of the correct type. When you reboot, you'll have to go into the BIOS setup again and load default values and save out of there. As it's not an Intel branded board, if you're still having issues with it after checking this, you're better off posting in the board manufacturers forums or emailing their tech support people. Good luck with the new battery!