arduino uno not responding

I've been running my arduino uno without problem since I received it last week - uploading sketches, etc. Tonight, I was experimenting with sending signals (using a blink sketch) from arduino output pins to a parallax i/o board relay input. I may have crossed wires or something because now when I attempt to upload a sketch I get the following message: avrdude: stk500_recv(): programmer is not responding The green ON light stays on but so does the pin-13 LED.

Should I try replacing the MEGA328P , the whole uno unit or is there a software approach to consider? By all indications, my linux is detecting the uno on /dev/tty/ACM0 but I just can't upload a sketch.

Thanks for any suggestions. lux11

Did you already tried in other computer?
Did you tried run arduino IDE as sudo?

Thanks HugoPT: I do not think the issue is related to my computer or the use of sudo. The reason is that when I upload a script using the arduino IDE, I can see the 'receive' LED on the board flashing as the board receives data. But evidently, the board is not communicating back to the computer - at least that is how I understand it. Also, previous to my encounter described earlier, I have been able to upload scripts without a problem. I'm hoping to get a replacement atmega chip to swap out and see if that makes a difference. In the meantime, I'm interested in knowing if there are any diagnostic tests I can come up with to track down the problem.