intermitent start up with radio cassette in my 2010 berliningo van?

the radio cassette ,has decided it will work only when it feels like , which is never when first start up in the morning , after about 20 mins driving the display lights up then I have to pull over leaving engine running and unplug and replug the multi plug on the back ,when this works (sometimes) all is well until I turn engine off then its same prob again ,any help appreciated .