|Please note that the suggestion of formatting is NOT recommended at this point since you have important data you are trying to save.|
You may be able to go to Disk Manager, right click on the drive and assign a letter. If this works then you should have access.
Formatting should be as a last resort and while data recovery may still be possible, wait for further suggestions before going down that road because we assume you will want to try to save all of the data and data recovery tools may not find all files (they are better on the more popular file types than the less popular file types).
You have to be a little bit crazy to keep you from going insane.