The worst case scenario is that the Checksum error is the result of a failed bios upgrade but then you wouldn't be able to enter the bios at all. Given you can still get there you need to boot from floppy via windows 98 boot floppy and run chkdsk C: and see if that hard drive is fubared.
Noli Nothis Permittere Te Terere!!
EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.