Format a locked external drive?

Ok, I have an old internal hard-drive that I want to use as an external back up drive for my macbook. It's an old seagate ultra ata that has been sitting in the garage for months. The problem is, I can't format it. I can transfer old files off it onto my mac, but I can't add files to it, or modify it in any way. I am trying to format it, and then use it with time machine. Anyone know how to format this drive? Is it even possible to do this?

The drive is more than likely formatted to NTFS. Your Mac can read the files and you can copy them but you can't write to the drive.

How are you trying to format the drive? Are you using Disk Utility? If you are, you need to erase the drive first then format it as FAT-32 (DOS) or HFS +.

Regards.