These are all server issues that you need to take up with your web host.
The 'SQL Server does not exist or access denied' error usually happens
if for whatever reason the SQL server can not be connected to.
It occasionally happens on this site and is often coursed by things
like network problems connecting to the SQL Server, the SQL Server
could be rebooting, or even over loaded.
The 'SQL Server error '80004005' Timeout expired' error is very similar
to the one above and is often coursed when the SQL Server doesn't
return data within the server specified timeout limit. This again is a
sign of network problems or an overloaded SQL Server.
With the amount of server related issues you are getting I think it's time you started looking for a new host.
You could try our own hosting, at
www.webwiz.net/webhosting