Turining SMART checks on in the BIOS does not "enable" smart. It only tells BIOS to check the SMART status of a hard drive at bootup and complain if it is (supposedly) broken.
SMART is completely done by the hard drive itself and it is up to the drive how many SMART functions to implement or whether to have the functionaility turned on or not.
Maybe you HD just doesn't have SMART or the temperature monitoring capability? Or, maybe the monitor program doesn't know how to interpret the temperature values of your specific drive?
Also, you cannot do SMART on RAID arrays. So if you have some fakeraid controller, it may be masking all SMART information.
You should use the definitive SMART utility - smartmontools to take a look at your drives and enable SMART if needed.