And did you format your USB Thumb Fat32 and set it up to Install UEFI GPT?
Win 7 SP1 HP should install, you need SP1 to support UEFI GPT
You may need to mod the boot file for the install also See
Rweben Thread on downgrade to win 7 insure you have win 7 drivers for your hardware Wi-Fi and Bluetooth particularly sensitive to drivers.
If you read all of that thread you will successfully downgrade to Win 7 with out much problem or issues at all
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro