leol:
Thanks for all your help. About "bypassing the USB" what do you mean? I have an arduino UNO and I don't know if that means I have a USB b port. Furthermore how would I replace the port on the arduino? Sorry for all the quetions but i am a bit short on money and do not want to have to buy a new arduino.
I am assuming the power is actually OK and the fault lies in the USB port, thereby offering a small chance of salvation. If the problem lies elsewhere, I assume there is no chance of salvation. Wiki USB. The type "B" port is the square one and common on Arduinos. It should be easy to unsolder it and a replacement should be about a dollar. It should be easy to cut the plug off a cable and solder the cable to the board on the four USB holes, thereby saving the cost of the port. You could even wire the cable to the underside connections and leave the dead port in place, but it would be better to remove it.
On the underside of the board, you may see near the USB port two pairs of little gold patches about 1x1.5mm. Both my Mega and my EtherTen have them. I don't know what they are but I bet they are test points. They might even be fusible links. You should inspect them closely for damage. If they are clearly damaged, soldering a new track over them may fix your problem.