SQL Server malfunctioning

Hi

Recently on our client's database server we experience some problems in functioning of SQL Server. Failures happen every few hours and so far we were not able to find clear explenation.

Clients (aplications) that are trying to perform some operations on database are receiving such error message:

 .Net SqlClient Data Provider: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)

Series of errors lasts about 60-90s and then everything goes back to normal working state. We matched time that we see errors occurring with two events in Windows Event Logger in Application section that are present every time communication troubles happen.

The Software Protection service entered the stopped state and Succesfully scheduled Software Protection...

At the same time in Performance Monitor CPU parameters we see that one core is working on 100% of it's capabilities (100% processor time, 0% user time) while other cores are about ~95% Idle. What is also worth to mention is that C1%Time drops to ~0 (about 1%) and C2%Time increases drasticly from ~50% to ~90%

Have you ever experienced any problems like that? What can be the main reason for all of this?