Doesn't find the arduino, but the arduino itself lights up when I plug it in.

There is a steady light on the "L" led, but when I try upload a example to it. I get the "avrdude: stk500_getsync(): not in sync: resp=0x00" error, and I know its not the computer since I tried another arduino and it works.

This happened after I did a project, where I connected an external power supply to the circuit. Is there some sort of fuse on the arduino uno ?