Problem installing Win 7 on a Win8/10 laptop with UFEI

Hi. I am looking for help with my Acer v3-571 Laptop. It came preinstalled with Win 8 and I later upgraded to Win 10. All my other machines use Win 7 and so I decided I'd like to install this on the Acer laptop when the time came for a refresh as I don't like 10, and like 8 even less so.
Before I started, I made a partition on the hard drive from within Windows, and in it I put all the files I was concerned about keeping. (This is what I have always done when re installing operating systems in the past.)
When I rebooted the laptop I couldn't get the Win 7 DVD to boot. I tried the usual changing the DVD drive higher in the order in the boot sequence etc which didn't work, so I changed the boot mode in the bios to Legacy, instead of UEFI which enabled me to boot the Win 7 install DVD.
I was able to get to the part where you can see the partitions on the hard drive and choose where you want to install windows. I opted to to format the partition where windows 10 had been installed, and then attempted to select this partition for my fresh Win 7 install. I noticed I was not able to select the partition, below the window which displays the partitions was a message: "Windows cannot be installed to Disk ) partition 4. (Show details) - (details: Windows cannot be installed to the disk. The selected disk is of the GPT partition style.) I then tried to make a UEFI bootable Win 7 USB storage flash drive using Rufus. This did boot, but only got as far as the Win 7 loading graphic before freezing.

So I am now in a situation where I am unable to install Windows 7, but I am also unable to restore Windows 10, as I deleted the partition. The recovery partition is still intact, and so when I boot the laptop (back in UEFI) it takes me into the recovery screens. However, if I select the option 'reset this PC', I am told that 'the drive is locked. Unlock the drive and try again', or 'Unable to reset your PC. A required drive partition is missing'. Can anyone suggest a way I can install windows & on this Laptop and Hard drive, or alternatively, can I put the hard drive in another PC and retrieve the files I need from the partition I made to save my files, and then format in such a way that I can then install Win 7 on it using legacy bios settings?

Thanks for any help in advance.

Hi, jmarket, and thanks for taking the time to reply to my message.

With regards to booting in legacy boot mode, I did actually manage to get Win 7 to boot from the CD by doing this. The problem is, because the drive is formatted for UEFI, It wont actually let me install Win 7 to the drive. However, it did let me use the 'format' button to format the main large partition where Win 8 was installed. This means I can no longer restore Windows 8. Furthermore, I made a partition on the drive whilst I still had Win 8 on it and saved all my stuff there. So I can't just stick the drive in another machine and format it, I either need a way to install Win on the hard drive with that partition intact, so I can access my backed up files on that partition when Win 7 in installed, or failing this, I need to put the drive in another machine and take off the stuff I need to keep before formatting it to use in legacy mode.
Any further suggestions would be most welcome.

Thanks