Does your 1420 have an accumulator under the cab, bolted to the side of the machine? There will be one hose going into it and usually a gate valve similar to what you'd see in your house somewhere with a handle on it.
Turn that valve off and see what happens. If it raises and stops when you release the button, it may be that the accumulator needs a smidge more nitrogen pressure. If so, you should be able to find the needed pressure somewhere in the service manual for you usual header size. Then lots of places can charge it for you. Most dealers, or any hydraulic outlet, even some welding supply houses.
If it dont stop with the valve off, you may have either a switch going bad or a voltage feedback issue somewhere over by the valve stack.