SQL 2012 Enterprise Edition only a CPU works

I just installed SQL 2012 Enterprice Edition in VM with 8 cores and 32G RAM. It seems only one core is used and others are idle when running SQL queries.

In the log file, the message is,

SQL Server detected 1 sockets with 8 cores per socket and 8 logical processors per socket,
8 total logical processors; using 8 logical processors based on SQL Server licensing.
This is an informational message; no user action is required.

I tried it to install into a desktop(not VM), all cores works while running the same queies.

Thanks in advance for your help.