Help

I just got a PS4, i use to have a ps3, im trying to sign in online with my account and it keeps saying my user ID or password is not right, or it will tell me im trying to sign into someone elses account which makes no sense because its mine... what can i do to get back online, it let me on for a split second, then i logged out and cant get back on... please help

Mike.

If you need my playstation gamer tag its Mizzum420_mnn