One other possibility is that your FET is up the swanee...if it's gone short circuit your LEDs (laser) would be on all the time.

This is going to be tricky to fix unless you have access to a Voltmeter (with ohmeter built in)...

http://www.uoguelph.ca/~antoon/gadgets/mostest.htm

As Irving says, check the Gate voltage for both your 'on' condition & 'off' condition.

(FETs can be a little unpredicatable with their actual 'cutoff' coltages vs their spec'ed datasheet cutoff voltage...it may well be the FET you have needs more than 5V to cut the gate off)