From yesterday SQL Server Service just randomly stops, I am not sure what is causing this to happen, but here is the Event Log on our server, we are using SQL Server 2008 R2
A fatal error occurred in the .NET Framework common language runtime. SQL Server is shutting down. If the error recurs after the server is restarted, contact Customer Support Services.
Please refer Microsoft KB article.. This is answer exactly what you are looking for.
http://support.microsoft.com/kb/981108