Lately I've seen issues with newer HP (G6, G7) servers not displaying the System Model correctly.  It usually indicates "System Model Null" or "System Model Unknown".  You may also find that the HP Server Agent service doesn't start and thus neither does the Foundation agent.  

These newer servers are outfitted with a iLO2 or iLO3 management processor.  Even though you may not use this iLO for remote control of the system, the agents use it to gather information about the server.  If the Management Processor Driver is not properly installed, the server agent can't start and thus can't properly report the system properties to the agents.

To verify this, Load the Device Manager and check the System Management node.  There should be two devices listed:

• HP ProLiant  iLO 3 Management Controller (CHIF)
• HP ProLiant  iLO 3 Management Controller (CORE)

or for iLO2

• HP ProLiant  iLO 2 Management Controller

If at least the CORE Driver isn't working or installed, you'll see the issues above.  To install/reinstall the proper driver, go to the HP Support and Drivers website and select the model of server and OS you have and download the latest HP Proliant iLO 2 Management Controller Driver Package or HP ProLiant iLO 3 Management Controller Driver Package for Windows under the Drivers - System Management section.  Once the driver issue is fixed, the agents should start normally and the System Model should show up normally.

Hope this helps.  Feel free to comment if you have any issues.