I think stormy13 might be right. I forgot about the Nvidia problems until he mentioned it. If it is one of those problem GPUs then contacting HP and Nvidia might be the best thing to do. Perhaps they would have a solution available. It certainly wouldn't hurt to ask.
As far as updating the driver
, it's a pretty straight-forward procedure. Drivers - Download NVIDIA Drivers
Enter the driver info from the drop down menus. Product Type: GeForce; Series: 8M (Notebooks); Product: 8400M GS; Operating System: Win 7 32-bit; your language of choice. Click the green Search button and follow the on-screen prompts. It'll take a few minutes for the scan to finish and your screen will probably flash on and off a few times.
Even if the driver update doesn't solve the problem you most likely won't be any worse off than you already are. Good luck and please post back if the driver update works or if you hear back from HP or Nvidia.