For future reference -
- Don't use 2.5" external drives
- Don't use enclosed external drives
- Get a Dock and a 3.5" Seagate drive
(Dock will run cooler, and have less complicated electronics)
For your current situation -
Get an external Dock (that is one where you shove a 3.5" drive vertically into it, and much of it is visible to you and to the air).
You don't say much about your external drive, but I believe most docks will also take a 2.5" drive
Try removing your drive from it's enclosure, and shove it into the dock. There is a chance that the electronics on your old enclosure are playing up.
It is worth a try.
If your drive was IDE, you can get a wee plastic thingy, with power supply, and USB connection, for reading your IDE drive. Under $10.