As soon as the ASUS logo pops up during post, spam the F8 key. You will then be presented with a window to choose your boot device. Select your installation media that has the UEFI prefix.

Maybe you didn't prepare your Windows 7 USB installer properly for a UEFI install.

does it have to be mbr or gpt?

You need to use GPT. If by some chance the XP941 is using MBR, you'd need to convert the partition to GPT.

Your USB drive must also contain the directory and file: "*:\efi\boot\bootx64.efi" (* is the drive letter of your USB key that holds the Windows 7 installation files). This is the ".efi" installation boot loader extension. If you do not have this directory file on your USB drive this is how you create it:

First, create a new directory called boot inside the "efi" folder on the USB. You will then need to copy all of the files from the "*:\efi\microsoft\boot" directory into the directory you just created ("*:\efi\boot"). Next, use 7-Zip to open the archive located at: "*:\sources\install.wim."

Inside the archive, find the file located in folder "1\Windows\boot\efi\bootmgfw.efi." Copy this file to "*:\EFI\Boot\" location you created earlier. (Not in the 7-zip) (This file is also available from any current windows 7 installation. It is located in the "C:\Windows\Boot\EFI" folder.)


After copying the file to the "*:\efi\boot" directory, rename the file in "*:\EFI\Boot\bootmgfw.efi" to "bootx64.efi". You should now have an EFI boot loader folder for Windows called *:\efi\boot\" with all of the files copied from the "*:\efi\microsoft\boot" folder and the newly named "bootx64.efi."
Your install media (DVD/USB) must be inserted into your PC prior to powering it up. This will allow your UEFI to register your device (DVD/USB drive) as a UEFI boot enabled device.