I can totally understand wanting a fresh install to make sure you don't have all that trial software and accompanying registry settings and appdata folders that don't go away even if you uninstall. Or if you wanted to go back to W7 from W8. But it can result in missing drivers and/or software for touchpads, special function keys, onscreen displays, etc.
If it is a new laptop, did it come with W8 preinstalled or W7? If it is a new model and came with Windows 8 then it is possible HP never created Windows 7 drivers. What is the make/model of computer?
It's also possible there was a BIOS update to handle issues. Did you check HP's site for the BIOS?