how can i upgrade my BIOS? there's a BIOS checksum error after the boot, i think its because my BIOS is not updated....i'm running a pentium III 600MHz processor...

Could you give a few more specs and details leading up to the problem? It could be hardware related and a BIOS flash is a last resort, even beyond reformatting.

Did you install a bigger harddrive that led up to it?

You probably don't need a BIOS update, you need a battery. CMOS Checksum Error means it lost its settings and needs to be reset. A temporary fix is to go into BIOS, make sure the basic setup is ok for hard drives, etc, then save changes and exit. Usually no changes are necessary, just save the dafaults and it should boot right. When the battery loses power CMOS defaults back to factory settings, which usually work fine. With a P-III the factory default for hard drive should be everything Auto, that works well in most cases. Sometimes you'll get a checksum error also if you change certain hardware, RAM does it most often.

If you shut the computer down overnight and it gets a checksum error again you can be pretty sure it needs a new battery. The usual battery is a CR 2032 watch type battery, about $3 in most department stores.

Check Components ID (http://www.pcguide.com/vb/showthread.php?s=&threadid=25502) for a picture of the battery if you don't know what to look for.