There is a couple of solutions, both requires to have only USB cable connected to a PC.

One simple, consist in keep reset button press together with power button, for some time over 20 seconds or so. If you are luccky you'll ear the sound of PC getting connected in safe mode. I've NOT tested this.

Second solution, a extreme one, that I've tried many times when my devices can't get connected thru USB and seems to be dead.

It's called the clip solution. This requires patience and a good hand.
You have to make a short-circuit while you have the device USB connected to a PC. Just don't get scared!! It will be safe if you follow carefully the instructions. It's similiar to the method explained in Romanian posted above bu Oma7144, but less tricky.

You'll have to locate the chip of main memory of your device (is a long black chip marked as Samsung of other alike brand). In enclosed pictures, it should be the black one to the left of metal frame. Just avoid the big square chip.

With USB cable connected to USB port in PC and to your device, just USB without AC connection in the device ... again, just USB. Then, run slowly a metal clip across the pins (little metal pieces that connect the chip to the board). Using the round part of the clip. Slowly, trying to make contact of a couple of this lot of pins to make the short circuit, keep your ear paying attention to the sound made from PC, when USB get connected in safe mode. It will connect without any damage to your device   

Try running along the pins in both sides of main memory. Just insist doing this... slowly. If you do thing right, you'll get connected.