External Hard Drive Not Working. Help please!

[superconfused]

This started when my computer wouldn't let me eject my external hard drive because it said it was in use. But there were no applications open, and this had happened before, so I just pulled it out. Then I plugged it back in and this message came up:

The disk "" was not repairable by this computer. It is being made available to you with limited functionality. You must back up your data and reformat the disk as soon as possible.

Now all the files are read-only and it won't let me copy most of the files or delete most of the files (error -61 message). Help!