The Monomachine and Machinedrum are getting on a bit in age, and this could lead to that the internal cable could get oxidation on its internal cable contacts. This, in its turn, can make the communication between the UI and CPU a bit unstable and cause several problems such as:
Occasional freezing either on startup or during use.
Strange characters appear on the screen.
The screen goes black.
All LEDs are permanently lit.
Open up the device, and remove every cable connector and then put it back again. Do this for all connectors on each PCB. This often helps to solve the problem.
If the problem persists or for a more permanent solution, you should get the connectors de-oxidized. We recommend that you contact a professional electronics repair specialist to help you with this.