Is the "tilt" switch pressed? I would expect it to keep pressing return if it is. So check that switch with a multimeter, and check the value on the pin it's going to with a multimeter as well. If the pin is low, disconnect the wire to switch and check it again.
If the pin is still low, do a sanity check by disconnect everything, upload sketch that does nothing but set that pin to be INPUT_PULLUP, and measure voltage on that pin with multimeter. If it's ~0V, instead of ~5v, chip is damaged.