I have a problrm with my USB 3.5 External Enclosed 80 GB HDD!

Well I bought 80 GB HDD, and my friend used it, but never removed it using safe remove, so now when I plugg it in, I can’t acces it, it makes everything slow, and I can’t open it. What can I do to recover my files, because i have at least 70 GB of files on it. Please help. Thanks in advance.