I certainly agree, getting a full sector-by-sector image is the first action you want to take once the drive is stabilized. But, before you do that, let's try to troubleshoot why the partition is missing first.
1. What is the model of drive?
2. What file system is it using (NTFS, FAT32, etc?)
3. Are you working with the drive in the enclosure or have you removed it?
4. When you power the drive on with your ear close to it, does it make any type of sound that could be the heads scraping against the platters?
5. How critical is this data?