help, my website allows closed cannot hold 2 users, error establishing a database connection, my website is down lost all users, help.

I am running ubuntu 16.04. with lamp 1 click install. I made before a month a good. It was working perfectly. But now if even I test my website page speed by any page speed tools I get the error. error establishing a database connection, really it is a problem. I did not find a solution to it. The problem it was working fine. I found error by utf firewall , I cannot remember the name but I disable it. I have many errors that cannot disappear.

[Warning] Changed limits: max_open_files: 1024 (requested 5000)

 [Warning] Changed limits: table_open_cache: 431 (requested 2000)

[Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).

[ERROR] InnoDB: mmap(137428992 bytes) failed; errno 12
 [ERROR] InnoDB: Cannot allocate memory for the buffer pool
 [ERROR] InnoDB: Plugin initialization aborted with error Generic error
 [ERROR] Plugin 'InnoDB' init function returned error.
 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
 [ERROR] Failed to initialize plugins.
[ERROR] Aborting

Please help. If you face this problem please help: