You should limit the memory SQL Server uses. In the SQL Server Management Studio, after you connect to the db server:
1. Right click on the name and choose Properties
2. In the Server Properties window, choose Memory
3. In this window you have Server memory options. Edit the Maximum server memory(in MB) to the value you think it would be appropriate in your case (i've set it to max 80% of the total RAM available, but you could adapt).
You have to restart the server for the setting to become effective.
Let me know if it helps.