HI, [PLS RATE if HELPS]
Pls refer the attachment for recovery procedure.
"Port Security" feature of CISCO IOS could have been enabled in GigEth3/1 and Violation rules could have been configured.
If the Rules was Violated the Port will be changed to Shutdown State automatically.
You will have to go for: Interface Configuration mode and manually bring UP the interface with "no shutdown" command.
PLS RATE if HELPS.
