Sometimes due to your BIOS/EFI you may find that you have chosen "Energy Efficient" for your CPU which may effectively disable turbo mode. This is because "Energy Efficient" will often restrict or throttle your CPU to the base speed. This can impact nearly any CPU such as Intel's, AMDs, Opteron, Xeon etc...
This is of course frustrating, for example if you have a CPU that is 2.0GHz base speed but turbo to 2.5GHz, you will never hit more than 2GHz.........