Can not read a floppy disk , but why?

I tried 2 separate installations of good floppy drives, with tests on good diskettes 1.44 size. The PC sees the device, knows the drive A: is there in Windows Explorer,
and even Norton utilties, can not tell me what is wrong. This is very puzzling. Ideas?
These drives work in other PC’s, with widows 95B just like this PC has. Help ?