ok to check the pressure switch.

with ignition off, check for continuity between the two oil pressure switch terminals on the vtec solenoid, it should show continuity if not then replace.

turn ignition on and check the voltage between oil pressure switch harness blue/black wire and ground. there should be approx 12 volts, if not then inspect for an open or short to ground in the blue/black wire between the connector and the ECM.

this reads the oil pressure which is what drives vtec and if it's too low hence i asked what oil pump ypu have then it may not read.
the engine speed, MPH, TPS, MAP, and coolant temp must all be correct for it to work also.

loss of power is either fuel or spark and if you are using a b16 manifold, fuel rail, FPR and p30 ecu it should have the right pressure from the fuel pump, check the filter esp if it's been sitting awhile. also if you tried to time it and did not jump the service connector then it's not in time. check it out and let us know this baffles me. atleast the CEL is a start so something isn't reading somewhere correctly.