MacBook pro mid-2010 WiFi problems

I am probably not the only one asking a WiFi related question, but this is a very particular one.

When I want to connect my MacBook to my 5Ghz network it tels me my password is incorrect, even though it is correct.

When I hit join a few times, it will connect. Until I close my macbook and it goes to sleep. After I wake it up it disconnected WiFi and I need to go through the same proces again. I've tested it with a 2.4Ghz network and it seems that that doesn't give problems.It also doesn't remember network connections, even for the 2.4Ghz network I need to provide the password every time. I tried reinstalling via CD (OS X 10.6, not that the problem started a few days back on 10.10.3) and it has the same problem even after erasing the disk.

How ever, I CAN successfully connect to the 5Ghz network on my iPhone and on Windows8.1

I am not sure what to do at this point. It is annoying not to be able to join a network (my home network I obviously use most of the time) normally.