is it showing any codes on display?
if you have access to the service menu you can look at the fault history and see whats been going on with the truck and the hours when it occurred.
usually when there is a fault with these trucks it will beep and a fault light will show up along with a display code. Since you say the display is not coming up properly you will have to either check the history once it does come up (since you say it does randomly) or you will need the zapi handset or the pc tool to get an idea of what is happening when it starts and faults out.