As stated in an earlier post in this thread, first check your server error log in the control panel and paste any error related here.
Also, more details are required. Same information needed as my other response
Shared hosting, VPS or dedicated server.
Version of mySQL
Version of PHP
HTTP server (Apache2, nginx, LightSpeed)
If on a shared hosting, it sounds VERY much like your node may be oversold (or they are having hardware problems). Same if on a cheaper OpenVS VPS plan (those get oversold often also unless you are with one of the big name providers. Dedicated Server and having problems then either hardware problem your your server settings a pooched.
It's almost sounding (from the types of errors you are having) that if you are on a shared host it's been oversold and you are running out of resources or the server is being taxed big time.