Dvd/Usb not runnning at boot for installation

Hi,
I purchased a new laptop of HP
Model- 15n-012TX . I want to install windows 7 over inbuilt Windows 8.
But when I insert DVD or Booted Usb ,It just cnt going to boot from it and general windws 8 starts.
I changed boot order and tested but still the same result...
stuck at it please help

Follow these steps to DownUPgrade Windows 8 to Windows 7

Once you've disabled Secure Boot you must boot the WIn7 installation media as a UEFI device in the Boot menu.

If using a flash stick it must be formatted from Option One in UEFI Bootable USB Flash Drive - Create in Windows

If after trying this it still won't install then try Legacy BIOS or CSM settings with UEFI Boot First. Every BIOS has different settings for this so you may need to post back a camera snap of all of those choices, or just list them for us to help you select.

Once installer boots you must delete all partitions during the Custom install.

If all else fails what always works is to Bypass UEFI to Install WIn7

I've not found any Win8 PC that can't run Win7. Manufacturers will try to scare you away from it since they are too lazy to build drivers or trying to enforce the Win8 phone app on consumers who overwhelmingly hate it. But drivers are almost all delivered in the Win7 installer or via Optional Windows Updates.

You only need to be sure to have your network LAN driver(s) in the backup in case it isn't provided during install, so you can install it, enable Automatically deliver drivers via Windows Update (Step 3) then run all rounds of Important and Optional Windows Update, with reboots, until there are no more.

This will deliver most other drivers, but if any are missing in Device Manager afterwards, google the device make/model or Hardware Identification for a Win7 driver, try the Win8 driver, use the excellent freeware DriverMax for it's scan and one free driver per day download, or ask back here in our Drivers forum where they can find any driver.