try holding play and do the reset. keep holding down play as the DJ starts up and you see rescue mode, select Disk Cleanup. Wait a few mins, the player will restart and you will see Rebuilding Library, hopefully it will work after.
If no go, Its a hardware failure most likely, the only option is to call Dell for a free replacement, dont worry about their refurbish talk, there is a high chance you will get a brand new DJ. Warranty status??
Try charging through the wall AC if you've been trying the USB, or the other way around. It might be a bad battery that doesn't take a charge, especially if it turns on when plugged to the wall/USB.