If you have C: to boot first and you get this message,it either means that you don't have an Operating system installed on HD,or the Boot sector is messed up.
To fix it if there is an OS installed,boot with good windows floppy,go to A: prompt and type "sys C:" without quotations.
and it should boot after that.
If your booting A: first and get this message,usually means your boot disk is messed up.or could also mean bad cable,hooked up wrong,or bad Floppy drive all together.
Hope this helps.
Shawn.