What is listed in the system properties, where all hardware is listed (dang, have been using Dutch version too long, forgot what it is exactly called in English)?
Have it search for new hardware if nothing is detected there. It is possible that somehow the drivers for this hardware have been removed somehow (and therefore can not be loaded).
If you see any exclamation marks in the listing you need to select properties at each item and select driver properties and reinstall the driver for this device, which can most likely be found on one the CDs provided with the HP PC.
ps ATI is the brand of the graphics card I think... (it is a manufacturer of graphics cards at least...)