Akhio

So it's been a couple of months since my navi screen went completely black in my 2008 IS250. I've had it for about a year now, nothing wrong until now...I've searched through threads, some have lead to an electrical problem, an alternator problem, or as simple as the codes need to be reset. So I ruled out the electrical problem due to the fact that every few weeks or so, the screen turns back on for a few minutes and has a "Power Consumption" start up screen. I went to 2 Auto Zones and asked for them to check my alternator and one said it was and the other said it wasn't. I'm not sure how to reset my Navi screen codes so I haven't tried that. Any help would be great at this point! Trying to get my screen back on for the winter because that's the only way I can change the climate. Also, the CD player and everything below works perfectly. Thanks so much for the help!