It is beeping because there is an error. If the control panel is blank, then that is where you start. See why the screen is blank. Did you have a power surge; did you go in the machine; what were you doing just before the beeping started?
I was checking the fuses and transistors with a multimeter
Unfortunately, I thinking you shorted something, but no telling what since I do not know what board you were on. If you get no green light on top of the head, then you probably shorted the main board.
Cannot provide any help - I do not do board level repairs for the same reason you are having. Trying to track down a short would cost you more than the board to replace.
You have a green light, when you go to turn it on - what happens - does it power up the control panel at least.
Again no help can I offer. It can be as simple as a cable or as complicated as a board. Once you start replacing components of a board you still can not safely rely on any other component. It may be enough to pass along a voltage, but you do not know if it is working at its proper capacity. Components, voltage, connectivity are the three variables that will keep you up at night. The ideal situation is to have a working machine and then swap out parts to see where the fault lies.