from your SET statement, it's looks like your trying to boot off the Slave drive, and /or have tried (possibly succeeded to a degree) installing on the slave.....or you took that SET snapshot just after booting from floppy.
Disconnect all drives except the Primary master (make sure the jumper is set to master) and the Sec master (CDROM), turn of both slaves in the BIOS, set CDROM as 1st boot device, make sure "use both IDE channels" is set in BIOS.
Disconnect all peripherals, except mouse, keyboard, monitor
Try again.
If using a 98 OEM see faq615-5157
If not, then Boot from floppy w/cdrom support
your cd drive will become E:\ (if you follow paragraph above)
change to E:\ from A:\ and type setup.exe
never hurts to run the HDD's Manu. diagnostics utility first....if you zero filll, then definitely run the diagnostics afterward before setup
TT4U
Notification:
These are just my thoughts....and should be carefully measured against other opinions.
Backup All Important Data/Docs