radio turns off after 4 mins

[sarb]

what could be the problem my radio turns off every 4 mins and black screen on mk3 ( i bought it over a year ago with same problem, wife never said anything about it so i didn't bother fixing it now my 4.8is goes in the garage for winter sleep i have the 4.4i for winter) what can i do to fix it not looking to spend 1k for mk4 + map dvd.

Please help

02 x5 4.4i
with factory nav upgraded to 16:9 wide screen (PO)

(i also posted in nav section i hope admin wont get angry)