There's a quick check for the on/off button. You substitute another button of the same type.
Go to the mobo header where the front panel connections plug in. Disconnect the two wires from the on/off button. Now move the two wires from the Reset button to the pins for on/off. This is the same type of momentary-contact normally-open switch. Power up and see if the Reset button will operate as if it were a normal On/Off button. If it does, you know everything is OK EXCEPT the on/off button switch.
So, now what? You can try to fix the faulty switch. You can replace it with something similar that fits. Or you can leave it as it is, using the Reset as On/Off, and having no Reset switch to use.