If I had to take a guess I would say that uefi cannot be installed as an upgrade. UEFI needs to be done on a fresh install of windows. While installing a UEFI windows 8 (I just did it a couple days ago), you boot your DVD drive from the boot menu (F12) into UEFI mode. In the boot menu you will notice your DVD drive has 2 options, you need to make sure you select the UEFI mode. Also make sure your BIOS is set to UEFI or Legacy + UEFI. If it is set to Legacy only you will not be able to boot UEFI. Windows setup pretty much looks identical to a normal install in UEFI mode aside from 1 thing. While formatting and creating "new" partitions on your drive, you will notice that Windows creates 4 partitions instead of 2. 3 of the 4 partitions will be windows reserved and recovery and you will have one larger partition for the actual windows OS. Lastly you will notice the drive will be formatted as GPT instead of MBR. This is also required for UEFI mode. Hopefully this will help you out a bit.