who knows, i got like 300gigs of music.
I would recommend the following course of action for now, then:
1) Check drive format as others suggested, it must be NTFS. If not - reformat.
2) If it's still not working and the drive has interfaces other than SATA - try them.
3) Still not working? Might want to try and update the drivers I mentioned before or go to step 4.
4) That's, of course, cumbersome, but you might wanna try selecting a bunches of directories from your 300Gb folder and copy them, set by set until you get an error. This way you can narrow it down to a particular directory.
5) Ah... just another thing, but that may take quite a while, you might want to leave it running overnight. Open a console (Start->Run->cmd.exe) and type in the following where you should use appropriate drive letter instead of X:.
chkdsk X: >> C:\chkdsk.log 2>&1
use it to check the SOURCE disk that you are copying from (where you have the 300Gb of MP3s), not the new disk - it is possible that the problem is in the directory you are trying to copy, not in the destination HDD.
This will run a disk check and create a log file in the root of disk C:. I don't know how long is it going to take, but it may take hours... Post the log file here.