Do you know what to do ?? It seems to be a common problem...
Hmm... There's a few common problems that can cause this...
Dirty drive? Try one of the 3.5" drive cleaner kits...
Floppy drive cable loose? Check the inside of the machine to make sure everything's plugged in well...
Floppy drive finally die? Floppy drive misaligned? (Have another machine somewhere you can run a known good disk?)
Do you have a virus checker? (Lamer exterminator or something mighta zapped your disks for you) Again, another machine to test on, make sure those disks are still good.
You need to make sure it's not a software failure before chasing the hardware, I suppose.