Don't worry! In your case, you should remember not to format this disk before you successfully recover all your important files back in case of any data.
The right thing you should do is to recover your data back before the format with the help of a disk recovery freeware. This free one has recovered all data of my friend from a WD 1TB flash drive, including 1478 pictures, 78work files and 20 videos. Is it great?
After the recovery process, you could format his drive to return its normal use without any hesitation. Important note: The overwritten original data can be gone permanently. You should remember not to save new file on this disk to overwrite the original data.
You should keep your important files backed up regularly on a separate drive or storage device in case of the similar problem.
Most of the time, it is caused by virus which destroy the file able and make the drive show not formatted message. So the first thing you may try is to scan the disk with some antivirus software. Microsoft essential and free AVG are good ones http://goo.gl/rx1KFq http://www.free.avg.com
After you make sure that the disk is clearn, you can scan the disk with data recovery software to recover files from the disk. see this step by step guide http://goo.gl/mIOJLp