Just recently I took out my external hard drive out of its enclosure case. When I put it back in, the drive seems to be "lagging" really bad, and sometimes freezing up the computer.

The only thing I keep on the drive is music files.

Are there some type of tools that may help me find out whats wrong? Hopefully this drive isnt dying. Ive got over 5 years of data!

Well after 5 Years of data, it could actually be full (above 90%) and horribly fragmented.
First off check how much space is available in percentage.

The other point is, that you may not have plugged the wires back in properly, you will need to undo it again, and re-confirm (by unplugging/replugging internal data cables)

Also after 5 years the drive may just be comming to the end of its life expectancy, and therefore grabbing (buying) a new drive, and backing everything up to it, would be most important, (As Mr. Burns says, "post haste")

Time to update to a bigger drive, and backup to it, I feel.

It all started when I removed it from the external, put another drive in, then put my original one back.

Ill definitely pickup another external before this one completely dies. or Ill tryout those programs

Thanks