Is it possible that an io pin dies if you set it as an Output, while an external switch forces it to direct GND?
I had the DDRx Rgister as Output and the PORTx to 1 (PullUp in case of Input).
The IO Pin does not act as output or input any more. The level is about 4,7V (VCC =5V), and does not change.
The other portpins on the same port are OK!