Input Monitor Button??

There is no input monitoring button. There's a screen to enable/disable input monitoring in the OPTIONS>AUDIO>Input monitoring tab. Highlight your sound card in blue. Then, close the box and hit the audio engine button at the top right of the screen - to the left of the yellow exclamation point. Sometimes input monitoring causes feedback (turn the audio engine button off to stop the feedback) or latency.

Rickenbacker, the input monitoring will drive you crazy, don't use it, I suggest getting a cheap mixer, behringer 802's are on sale at guitar center for $49 you can monitor from there and not get the delay. and hear the guitar in real time.