How to fix my 08 Honda Civic blank black screen GPS Navi/Radio screen?

Just blacked out 2 days ago and no buttons work but I can control it on the steering wheel

Try to disconnect the battery cables and touch the two cable's ends together for 15 seconds or so. If you need to reset the radio or the NAV system afterward. This may help:
https://radio-navicode.honda.com/...honda.com/

This is for your reading, see if it give you some ideas:
http://www.driveaccord.net/forums/showthread.php?t=9540

It doesn't work