Uno will not connect after blink program and battery pack

I just bought a uno and ran the first program blink.
disconnected it from my laptop and plugged in the battery pack and the program still worked.
Started to do a second program and now the uno is not a recognized devise.
In the Arduino software under tools, the serial port option is dimmed out.
Whats the deal? I have a group of students that will be doing the same projects this summer.
Do I break it?



Got it
I think my usb on the laptop is bad
If i move the wire it connects now.
Is this common?, as I will have a room of kids working on this hardware over the summer


Try a new lead -

Is always good advice. Even the connectors on good quality cables will eventually fail. :wink: