Floppy drive query

I have a bit of a puzzle here. I have a floppy drive that reads / write from a disk, but wont format the disks. I’ve replaced the drive with the same results. I’ve also checked the floppies in 2 othere systems & they format fine.
Everythings register ok in the bios, & used to work fine untill recently. Thinking it may be a program etc thats affected the system I re-installed (win98SE). The results are the same.
Any ideas?