Power on are compressor, hear buzz, but pump did not start .

There is an unloader valve and a check valve on the discharge side of the pump. The check valve is not holding and the unloader is not dumping the pressure so the compressor cannot start. Since it is new, you may want to take it back. If not you are going to be replacing parts.

3 inch pulley with a 3600 rpm motor. 6 inch pulley with 1800 rpm motor.

The pressure regulator on an air compressor is designed to let the pump motor run until the pressure in the tanks reaches their safe level. While you are using the air the pressure drops in the tanks until it reaches the level where the pressure switch turns the motor on again and refills the tanks to their rated level. The pressure where these two things happen is usually with in ten psi above or below the rated levels because few regulators are so precise and are affected by temperature that they turn and off exactly at the rated pressures. If a pressure regulator is damaged or broken it is possible for the tank to either reach unsafe high levels or not turn on when the pressure drops to where it should restart the motor. If you are in doubt, have the regulator checked or replaced as overpressured tanks are very dangerous.

If your compressor is oil-less type, most likely pressure is leaking past piston ring. To verify, remove cover to expose bottom of cylinder (unplug compressor and let out all air). With flashlight, examine the upper-most part of the cylinder (turn motor by hand till piston is at top of stroke). If top of cylinder is scratched, then pressure is leaking past.
For many years now, stores are in a race to have more HP and PSI to attract customers. Customer is really the loser because components used to make the units can not handle the higher pressure. Normally small 115v compressors are set to cut out at 125psi and larger two stage units will cut out at 160psi. Small compressor set to 200psi makes for short lived compressor. Could be compared to driving your car at 100mph all day every day. Longest life is attained when unit is being used at about 60 to 75 % of capacity.
To allow your compressor to reach cutout pressure and keep working for a while, lower cutout to 120psi (pressure switch may be adjustable). To restore to 200psi, replace cylinder/ ring.
If your compressor is oil type, suspect leaking reed valves.

I would guess from the info supplied that the pressure switch is shutting it down at 125. Most piston type compressor only pump a max. of 175 unless it is a special high pressure unit. Also it may be shutting down on high amps, high temp etc.However with all that said Piston units are positive displacement, meanning that it should pump until something gives. Start your unit, close the discharge air valve and see what it pumps up to. May have to adjust pressure switch to get over 125. If unit runs and runs and just will not go over 125, you probably have a valve going bad. Do you have a safety lifting. if so another indication of a bad valve.

my ace air compressor which is 26 gallon 5 hp will not get over 60psi what is wrong with it please?

sounds like the pressure switch is fused shut, more than likely it needs to be replaced, most single stage pumps should shut off at 125 psi max.

you could check the bleed valve.
it is located under the tank,
put on the unit and place your hand over the valve,
if there is air coming out of it then that is your problem.
some valves are made to tighten and some are made
to loosen. important stop the air from coming out.
if that is not the problem contact me for a next tip.

Yes,but if the max is 125 you don't want to increase it above 110 and set off the pressure relief valve.