strange behaviour of pentium 60-win98a

my customer tells me that he cannot boot the drive, even the system-disk does not boot. floppy is activated and is 1.44 in cmos-setup.
hdd is activated and-hopefully-the data have not been changed. computer is not on internet. no virus. here is the error: unvalid system, change data-carrier.(in german: ung?ltiges system-datentr?ger wechseln.
we have checked the system disk and have booted from it.
can i use a win98se-bootdisk and try to make fdisk /mbr and/or sys c:?

if nothing helps i will recopy the drive, after testing a second drive on the machine.