need help with external hard drive set up

today my hard (I've been using for six months) says it's not a recordable devise when I try to open a session. This has happend before and I found the answer to the problem here in the forum, but I can't find the thred this time. Like an idiot I didn't save it. It has something to do with going in and changing a setting in the computer. Can anyone help please. Clintone

It's a permanent thread at the top of this forum:

I'm an idiot.............thanks