Problems with bootmenu

When You Restart your pc , as soon as acer logo appears there is key you need to press written down ( generally F2 , F8 OR Delete) , Then you Enter into BIOS , Go in Boot Order (Preference) then Select USB-HDD (something like that) and Bring it at top ( usually pressing F5 or F6) , Then Save and Reboot.
It would boot from USB.
 

did this but it still booted Windows 8
 
1) Download Power Iso Free Software in Windows
2) Run in Administrator Mode (By right click and run as admin)
3) Go to tools and select option create bootable usb drive
4) In Source File Choose the ISO from where you have saved in Hard Disk in Destination Drive Select the USB you want to make bootable USB.
5) Click Start.
6) When Finished , Restart Computer , it will boot With os in USB.
 


I did all u said but it didnt boot with the usb