I can't access part of my external hard drive

Hello!

I have a Seagate 1 terabyte external hard drive. I use Linux Ubuntu although I am not sure which version. The 10.04 one maybe? Or the one before?

Anyway. I cannot access one file on the hard drive. I have used ~500 GB up, and there is nothing in the trash.100 file. I have added up the amount of data in the other files, which comes to about 130GB. This means I can't access the other 370GB :/

It looks to me like the files are there but somehow hidden from view from me (I already tried "show hidden files" but they're films, so shouldn't be hidden anyway).

I don't know how to program on computers so if I could have an idiot-proof guide to what to do, that would be most useful.

I've also not dropped or damaged my hard drive in any way recently. I just leave it plugged in all the time and it's usually fine. It's just been the past 4 or 5 days that it's been like this.

Can anyone help me?

Thankyou!
Carol xx