|Look in 'Computer' and see what the drive shows as its capacity and if this coincides with what it should be.|
You can try Recurva to see if it finds any files on the drive that are not showing up now. It is highly recommended here and the one time I needed it, it found more info from an old USB hard drive (installed as an internal drive) than anything else was able to. I have found that it is better at common file types like pictures, music, Word files and was not able to recover Photoshop & AutoCad files (at least in this instance).
If you had more than one partition and one does not show up and that is where your missing files are, first try Recurva. If it does not find anything from that partition, you may need to repartition that area on the drive and then use QUICK format (NOT full format) and try Recurva again. That is how I was able to recover what files I was able to from that older USB drive (though I installed it as an internal SATA drive to have better access without the external's circuit in between in case that was the issue).
You have to be a little bit crazy to keep you from going insane.