The way to be sure that the lowering solenoid isn't being commanded on is to disconnect it at the solenoid. Not sure about your exact model but most I've worked on have a black plug on the lowering solenoid that's held on by a screw in the middle of the plug. Just disconnect.

To check the lift cylinder, put a gate valve in between the pump and the lift hose. Lift up and then close the valve. If it continues to lower then you've got bad packing. If it comes to a stop, then the lift cylinder is doing its job. The lift cylinder also probably has a blow-by return tube made of clear 1/4 in plastic. If you see a steady stream of oil going through it as you lift that would also indicate bad lift cylinder packing.

The solenoid valve can be stuck open by debris in the valve. Sometimes you can fix it by cleaning. But watch out for springs as you disassemble.

Model# w45Z-HD
serial number A419C04582
I have checked the wiring everything looks okay in inside the control handle.
I have even disconnected all switches and the same thing happens after i hit the hydraulics to lift starts to lower on its own. I recently been testing the hydraulic motor and would make weird noises and then after a while it started smoking and then it would not work anymore so I thought great that was the problem all along. I replace the hydraulic motor only not the pump. New one was installed I was really excited because I was for sure that was the problem but after Installed it the problem continued. should I inspect the lift cylinder next or the hydraulic lift pump?

having a serial number would be helpful.
but having said that, most of these units have a low and high speed lift switch on one side of the handle and low and high speed lowering switches on the other side, since you said you hear the motor humming? Is this without pressing the button on the handle? You may want to check those switches, remove the cover off the handle and check those, check the wiring and make sure nothing is pinched. it sound like one of the buttons are stuck, if one is that may cause an unexpected action like lowering because of a stuck button or two?
If that handle has been taken apart at any time in the past it sounds like it may not be assembled properly?

If what lumber jack told you after that it is possible the cylinder packing is bad and will not hold also if you have a hand set you could look at the switches and work them and look to make sure they work correctly.

I tried it and same thing still comes down Im checking the valve sialoid might have a bad one thanks

It could be that you are lifting and lowering at the same time. Could be a stuck lowering switch. To diagnose disconnect the lowering solenoid and try to lift.