This effects all the SQL server jobs connecting to this server, and all users connected. So for users we have both Management Studio, and .Net Apps.
A key here is: when this happens, can you connect locally? That is, if you have SSMS running on the server, can you connect to SQL Server from this local instance of SSMS?
If you can, and everything else is locked out, it seems like a network issue. If you cannot, it is more likely to be a problem inside SQL Server.
Have you checked the SQL Server errorlog for messages related to these incidents?
Erland Sommarskog, SQL Server MVP, www.sommarskog.se