2 HDs, 3 shown in my computer

I just got an Asus a7a266 and put the 2 HDs from my old sys on, running 98. Now it shows C: as the main drive, D: shows 0 used and 0 free, E: as my backup and personal stuff drive and the CDROM as F:. the drives were shared when the switch was made,that’s all I can think of. there is also an “unknown device” I cannot figure out.
Any thoughts?
Thanx