SQL 2008 Developer Edition, not using all CPU´s

My SQL Server doesn´t want to use the second CPU for our Vault database. I tried to use different configurations for the CPU affinity in SQL Management Studio, but doesn't seem to fix it.
I've read an article about different values for affinity mask but I'm not sure which values are correct, the article was about 4 CPU´s and someone suggested to set the config value to 15.
My Values for affinity mask are min: -2147483648; max: 2147483647; config_value = 0; run_value = 0;
The server is virtual server.

Thanks in advance

Check the SQL Log Viewer in SSMS from the last time the database service was restarted, it will note how many CPU's are detected; and like @Aaron Bertrand noted, be sure you are running queries that will take advantage of parallelism, and that your MAXDOP is set correctly.

StackExchange Database Administrators Q#15942, answer score: 2