It should have found something.
In fact, a lot of things.
Even if brand new, it was run on the factory production line and all of those deleted files should still be there.
Try this:
http://www.cgsecurity.org/wiki/TestDisk_Download
When/If you are asked if the partition table is 'Vista' - answer yes.
It most likely has not been jail broken before if someone went to the trouble to wipe the USB storage area clean.
You only choice right now is to use the serial port jail breaking.