HDD Error during Hard Boot only

I am recieving an error, that say’s, “HDD Error, PLease insert boot disk”.
This only happens if I turn the system off and then back on. If I hit the reset switch, everything operates perfectly fine. Why does this only happen during a hard boot withthe power switch.
The system is an older P233, Win98, 1.2 gig WD, 32 meg, ATX
Any help or suggestions is greatly appreciated.