Hybrid ATI CrossFire™ Platform(Onboard GPU + 1 discrete GPU) Requirements:
The requirements of a ATI Hybrid CrossFire system are:
ATI Radeon™ HD 2400 Series, ATI Radeon™ HD 3400 Series or ATI Mobility Radeon™ HD 3400 Series graphics processor
ATI Radeon™ HD 2400 supports only ATI Hybrid CrossFireX™ technology and ATI SurroundView™ technology.
A motherboard based on an AMD 780G or AMD 790GX integrated chipset
Windows Vista®
If you meet all the requirements I would download GPU-Z and check if crossfire is turned on.
You can also get CCC (Catalyst control center) from AMD's website. I can turn on/off my crossfire from that location.