DMVLS600HL

Hey good ppl. I'm having an issue with my Nav system. I'm not sure if its going out or if it's due to the cold weather but it doesn't immediately come on when I start the car. At some point while I'm driving I'll notice that it's on and working but it seems to also be intermittently switching between the day and night time screen mode. Any advice on how to check to determine if it needs to be replaced or if there is a fix? Thanks in advance.