After installing Win8, you can't install other systems. How to do

After purchasing the computer, the WIN8 X64 system is pre-installed. But I don't like win8, so I want to use WIN7 instead. But using the WINDOWS PE boot disk, when trying to enter the PE tool, it can't be entered anyway. The same is true for the U disk version of WINDOWS PE.

For this problem, the preliminary estimate of Xiaobian should be caused by security settings. Boot into the BIOS, modify the following options, the problem is solved, the steps are as follows:
1, restart the machine, enter the BIOS;
2, enter the security & mdash; > secure boot option, set its value to Disabled;
3 Enter the Startup— UEFI/Legacy Boot option, change the value of the UEFI/Legacy Boot option to Both; then select the UEFI/Legacy Boot Priority value as UEFI First;
4, press F10 to save and restart the computer, plug in U disk version PE, OK. I can finally enter!