What the $#@! happened to my music???

I'm sorry if this is wrong forum, but kind of overlaps....I had moved a bunch of tunes form WMP to a file on the external drive. I had them in my WMP AFTER that, I've been listening to them. Today, it says it can't find the files. The music is still there, played it on Winamp, & moved 2 files back to the C drive (where space is limited, that's why I moved them), & they play fine in WMP. So what is it's problem? Help!!
Yes, it must be plugged in right becuase I can view everything on the external drive.
Windows XP
Western Digital 2 TB external drive.
Thank you...Pulling out my hair here!

 

make sure the drive letter for the 2tb external drive is the same as it was when you moved the files from WMP

or rebuild the playlist

 

It's working again...... I dont' know what happened.:confused