And your certain that you have the same version of Windows that you did before, prehaps XP Home now where you may have had XP Pro before? These are the only two things I can think of that would cause that partition to appear as "Unallocated". Either it really is unallocated and the partition at some point has been deleted or the file allocation table is not found or no longer recognised. If you have a friend with XP Pro or Vista on their PC, it may be worth trying the disk on their PC to check for certain.

Its XP Home... I used the same Dell CD's that I've used to restore every other time.

OK, as long as your absolutely sure, however the question remains what has caused this disk to appear "Unallocated"? If it wasn't deleted, then the only remaining cause, however extreemly unlikely is that the File Allocation Table was being written to at the moment it was disconnected, or there is a physical problem with that area of the disk.

In any case, the next stage would be to attempt a recovery. The mothods of recovery depend on how valuable the data is on your disk, and how much you can afford. It's important in the meantime not to play around with the disk, try to create new partitions and such as this will reduce the risk of recovery.

The best chance of recovering your data is to send the hard drive to a data recovery service such as Data Recovery: Crashed hard drive? Lost data? ADR Data Recovery recovers critical business information! . These generally cost more, take longer, but have a highest success rate than any other.

Another option is to use data recovery software. The best software I've used is called R-Studio which works very well, but still comes with a price tag. File Recovery and Data Recovery Software. Hard Drive recovery utility

Hi Relay, I agree with what Mad Monkey has said. Just try plugging your external drive into other system, if it is easily accessible no issues. If not, then you have a problem here. May be you have unknowingly deleted the partition or just formatted it. Don’t worry! There are hard drive recovery utilities that are available. Some are extremely reasonable and you can give them a shot. I personally suggest you to try NTFS Data Recovery Software since your drive had XP Home.

Hope this helps you.

Makred as Answered