I have a HP Pavilion G6 2215SO. As you may already know, HP has tons of bloatware in their computers. And Windows 8 with their bloatware just doesn't work for me. So I thought about it and bought a Windows 8.1 PRO ISO file. I made a bootable USB with Windows7 USB/DVD tool and tried tom install it on the laptop. What I didn't know was that my laptop is running UEFI. Because of that, my usb didn't show in "Boot options". I could only see OS management boot something and boot with EFI file(I tried editing the boot order, didn't work). I did some research and enabled legacy boot. Now I could see my usb and continued. I chose Custom Installation (I wanted to install the new Windows on a separate partition). But the problem is that I can't install Windows, because "the selected disk is of the gpt partition style". I tried deleting, reformatting the partition but it didn't work. And now I don't know what to do.

A Legacy-based boot media (the bootable USB drive that you have created) cannot be used to perform a clean install of Windows 8 on a UEFI system. For this, you need to create a UEFI bootable USB Flash Drive of Windows 8. You may follow these steps to create a UEFI bootable USB installation media manually on your Windows 8 computer and then boot from it to clean install Windows 8 in UEFI mode.

a) Press “Windows Logo” + “X” keys on the keyboard and select “Command Prompt (Admin)” from the list.
b) Connect the destination USB flash drive to the computer. c) In the elevated command prompt, type the commands below one at a time and press “Enter” after each command.

Diskpart
list disk

d) Now, make a note of the disk number of the target USB drive which you have connected.
e) In the elevated command prompt, type the following commands one at a time and press “Enter” after each command.

select disk #

(Note: where # is the target USB drive noted in step d)

clean

create partition primary

format fs=fat32 quick

active

assign

list volume

exit


f) Make a note of the volume letter assigned for the USB flash drive in the command prompt.

Now, you need to extract the .ISO file of Windows 8 and then copy all its contents to the newly created UEFI bootable USB drive. Follow these steps for the same.

a) Open File Explorer and navigate to the location where you have saved the Windows 8 .ISO file.
b) Right click on it and then select “Mount” from its context menu.
c) The mounted .ISO file will now automatically open and then select all files in it, right click and then send them to the UEFI bootable USB drive. This may take a while.
d) Now, you have created the Windows 8 UEFI bootable USB drive which can be used to boot from to perform a clean install of Windows 8 on your computer.