DE2 Quartus debounced circuit

you shouldn't use the push button as clock input, it isvery unreliable and sensitive to bounces, as you discovered.

Instead, use a regular clock (I'm sure the board has an oscillator you can use) and monitor the pb signal on each clock cycle. You can detect a change on the button status by comparing the current value of pb with the previous one. You will also probably need to implement a delay for proper debouncing.