Fix Connection Issues with Oracle 12C Database

I cannot connect to my Oracle 12C database after importing backup files. When I try to connect using SqlDeveloper it says "Listener refused the connection with the following error: ORA-12528, TNS:listener: all appropriate instances are blocking new connections" I need someone who can help me connect to my database with all the information there. If you know what you're doing this should only take 30 minutes maximum. I have TeamViewer so you can have direct access to my PC. My operating system is Linux Debian 8 64 Bit.