Did you reformat it with FAT32 maybe? Is it only on the external drive, not in the computer folders?
It is the external hard drive, the girlfriend was messing about with the security settings and it's locked everyone out including myself the administraitor. When i click on properties the security tab has gone?
Ah, any clue what she did then? You'll have to undo the settings. To turn off the security tab you probably turn off file sharing, or maybe changed a system policy.