I have been trying to install Windows 7 all day with no success. At first, it said that the current system policy is blocking the DVD. I figured out that it was the Secure Boot and I disabled it.
Now the DVD boots but it hangs on the first loading screen which says Starting Windows and the animated Windows logo. I believe that it's something to do with the UEFI because it boots using Legacy Mode normally, but it won't install Windows 7 while Legacy Mode is on due to the presence of GPT disks which require UEFI to be enabled during the installation.
I would also like to add that my Windows 8 DVD only boots wihle Legacy Mode is enabled and it shows "No bootable devices found" if I select UEFI.
Please do not recommend me to erase the disk as I have important files on the disk and not willing to do this. Any help will be greatly appreciated.