Yes, I tried that just now, but the situation remains the same. It appears that the drive got un-formatted somehow after I unplugged it. I tried to re-format it, but I keep getting the error message "the format did not complete successfully".

I have an old external hard drive which I plugged into my USB for the first time last night, and it was recognized by my computer, and was full of files my friend put on it for me. Today I plugged it in and the computer can't find it... Well, the disk manager recognizes it (as apparently empty, and ...