Hi:
HP does not support their consumer PC's for any other Windows operating system but the current one in place which is now W8.
First, I recommend you make your set of W8 recovery disks in case your attempt to install W7 is unsuccessful, but also messes up W8, leaving you high and dry as it were.
To Install W7 64 bit, you need to go into the BIOS and enable Legacy Mode and disable Secure boot.
Then you should be able to install W7 x64.
Next all the W7 x64 drivers and software from this older model should also work on yours.
DO NOT USE ANY BIOS OR FIRMWARE FILES