What version of nopCommerce ?
What is the server configuation - shared ?
How much memory does the server have ?
Your error messages indicates the the time out is due to the SQL connection.
Where is your DB server? (on same server as the web site or another? on same LAN?)
Database and website on the same server
Also, the error message says it is occurring when "starting the application".
Is your web site restarting often? Check the IIS logs to see if any errors - e.g. the app pool is restarting.
Is the SQL server always running?
Does the SQL timeout error also occur at other times (not having "starting the application" in the message)?