Oil pressure
Coolant temp
Speed sensor

Those three things need to be opperating/working order for vtec to work. I will also add that it's not very easy to hear vtec in a single cam like a B-series or H-series motor.

Check those things, if every thing seems fine, the vtec solenoid screen may be clogged, check that. Put a test light in-line to your vtec solenoid and see if it lights up when vtec is supposed the engauge.