Launcher problems

After opening League, I can get into the log in screen and play. But, after I close NA and switch to PBE, it opens the PBE and I can log in, but if I go back to the NA, it doesn't open. After opening League, the 'League of Legends' sign stays for a few seconds, and then a black box appears behind it. Then a message saying PVP.Kerrnel has stopped working. I ran it as admin and made sure no other League was opened in the background. But, after I restart I can go back into the normal servers, but it repeats if I log out and switch. How do I fix this?