Taking input by expansion header

You should not touch the pin with your hand, nor leave the wire unconnected! ;-)

Anyway, that's happens because you need to use a pull-up (and possibly a capacitor) or any other method to set the input to a well defined level when it's not driven.

I don't have the DE1 board schematics here, but I guess it directly exposes fpga pins. Then you can initially try to enable the pull up resistor internal to the fpga.

However, consider that this is a weak pull up, usually equivalent to a >100k resistor, so it's possible it will not solve your problem completely.