If you removed the hydraulic transfer cap to put oil in it is common to not place the Standpipe back in the pump correctly.
Set the the three point draft in the up position, and the lift control lever in the transport position, remove the 3/8 " national pipe thread plug on the side of the lift cover (right front) above the transmission dipstick.
IMPORTANT PULL THE ENGINE STOP OUT SO THE ENGINE WONT RUN and crank the engine while observing that port you just opened. Oil should come out of the port.
If oil does not come out, pull the key so you do not get an accidental bump on the starter, drop the lift arms, remove the transfer cap that is held on by two setscrews (located above the plug you removed). Once the cap is removed you should see the hydraulic standpipe exposed about 3/8 inch. If you see nothing but a hole the standpipe has fallen inside.
If that is the case remove the right side plate (one with the transmission dipstick). Insert your hand in the access port you just opened, and reach forward. You will feel the pipe that is approximately a foot long. Line it up with the hole in the cover at the top, pull it out and and replace the O rings. To reinstall the standpipe it is necessary to reach inside and locate the hole in the pump where the pipe inserts, line the pipe up with the pump, and give the upper end a light tap to press the lower O ring into the pump. Install a new O ring on the underside of the cap, reinstall the cap then button everything up and you should have pressure.
If you did not install new O rings on that pipe when you installed the pump the same process will be followed to pull the standpipe and install new O rings. Just will not need to fish for the pipe, but will need to use your finger in the pump port to locate and fish out any old or broken O ring.