Boot to bios, usually tap <DEL> key on post.
Usually CMOS setup
Make sure Diskette Drive A = 3 1/2inch
Usually Advanced Bios Features
Set first boot device to floppy
Insert any old floppy
Save and Exit
If it is a non bootable diskette, then hopefully you should get 'non system boot disk'. What this would mean is the floppy drive works, if it ignores the floppy disk completly the drive is not plugged in correctly or faulty.