"Drive is nor Formatted" Error for External Hardisk

Sorry if this is the wrong section to post this in, but recently I was using my external hardisk, when suddenly I get this error message telling me that the drive is not formatted, and giving me the option to format it now.

Obviously this isn't something I want to do as there is about 300gb of data on here that I don't want to lose. Any suggestions on what can be done?

Drive is a Freecom 1TB SATA drive, im running WinXP SP2 if that's any help. Drive also had no partitions on it if that helps.

Sounds as though the drives Partition Table or Root Directory may have gotten trashed. There are various drive/data recovery programs that can help, such as something that has an "un-format" command.
It could also be a problem with the USB adapter in the external box. You could try removing the actual Hard Drive from the external box and hooking it up to your computer or in another external enclosure, to see if the drive is actually ok.

yeah, I would try to connect it directly to your PC like Quaker said; if that doesn't work you may be able to recover your data via a software tool.

Alright I've run some various programs to rebuild partition tables and boot sectors, they all say that they're fine. However after running a full scan I was relieved to see all my data was there, this revealed to me what seems to be the problem. The drive is over capacity. I got back results like 966gb/931gb which is obviously impossible.

So does anybody know of some program I can use to delete some files off the drive without being forced to do the windows solution and trash it all?

did you try defragging it? you should never let a hard drive get over 80-85% capacity btw... it won't run nearly as fast once it tops that % point.