cannot connect again after 15 minutes

Hi,

I have SQL 2005 full version installed a remote server and when I start my computer I can connect to the database from SQL Managment Studio and a program I'm making. After about 15 minutes I find that I cannot connect using both programs, but if I enter the servers IP address using Managment Studio I can connect (this does not happen with the program I'm making). I have to log of my computer before I can connect again.

Anyone having the same problem or how to fix it

Thanks

PQSIK