Weird arduino problems

my arduino uno r3 was working fine until yesterday when it was not receiving any power through usb. i could not upload any programs even with nothing connected. when i power it with a 9v battery, it works fine but runs only the old program. please help

Have you measured the 5v when using USB?


  1. try another USB port
  2. try another USB cable
  3. check soldering joints of arduino USB connector

Looks like this is another of the "join, ask one question, leave once problem solved without response" types.