considering Maxtor went out of business in 2006 (bought by Seagate), that would make your drive at least 6 years old. Considering your average drive has a life expectancy of 5-7 years (and portable drives shorter than that due to travel), it is most likely that the drive is dying.
remove the drive from the enclosure, install it inside of a desktop, and copy anything important off of it and onto a newer drive (or at least one that is not failing). Then run some tests on the drive to make sure that the drive itself is bad, and that it was not the enclosure that died on you (because that happens a lot too). If the drive is fine, then you can continue using it either as an internal drive, or by purchasing a new enclosure for it.
But like I said, it is likely nearing the end of it's lifespan, so I would not trust it with the only copy of any important files from this point on. Time to buy a new external drive either way.