Downgrade Windows 8 Pre-installed (UEFI) to Windows 7 and hibernation

[Kairoz]

Hello, English is not my native language, so... if something is confuse tell me.

I've got a Dell Inspiron 5558, here's driver download page: Product Support | Dell US

It came with Windows 8.1 pre-installed and I wanted to downgrade to Windows 7.

So I've got a Windows 7 iso and use rufus.
Also I changed UEFI settings to: Disabled secure boot and enabled legacy.

I could boot Windows 7 installation setup and I installed Windows 7 and works great!

But there's one detail: I didn't erase all partitions in any point like every tutorial said.
When I hibernate my laptop and then turn on again, it can't came out from hibernation the error code is 0xc0000000d

I would erase all partitions and reinstall Windows 7 but I don't want to lose Windows 8 factory image or OEM partitions. I want to turn on my laptop and see Dell logo. But I don't know how to backup these partitions and restore.

Also, if I change UEFI settings for anything different of above settings, Windows 7 doesn't boot.

What do you think?

 

[Megahertz07]

Disabled secure boot was correct but to set UEFI to Legacy wasn't. Windows 7 can be and should be installed as UEFI.
Can you still boot Win 8.1 or does your BIOS has an app to create default factory restore disk (or on USB media)?
This is what I would do:
If you do have personal data on Win 7, back it up.
Find if BIOS can create factory restore disk (or on USB media). If it does, create a factory restore disk.
If it doesn't, restore BIOS settings to factory default (secure boot and UEFI) and then restore Win 8.1. Once restored, launch a Dell app to create system restore disk (or on USB media). There are many reasons to create one: HDD failure, virus, mistakes etc.
Once you've created the system restore disk, test it, at least, if it boots.
Now that you've created a backup that you can trust, Install Win 7.
- A SSD is the major tech upgrade that you can give to your laptop. The size depends on your budget and what you have to store in it. You can buy a 128 GB SSD for US$ 50 PNY CS1311 2.5" 120GB SATA III TLC Internal Solid State Drive (SSD) SSD7CS1311-120-RB - Newegg.com and put your HDD on a USB doc. Boots in 20 seconds, and opens programs at a blink of an eye. I strongly recommend.
- Disable secure boot and keep UEFI.
- Boot on the Win 7 installation disk on UEFI option, go advanced, delete all partitions but the Dell recovery. Normally it is the last one and is about 15GB in size. When done, you're going to have two partitions. Choose the first and then New. It's going to inform that it will create two more partitions (UEFI boot loader and MS reserved). Select the third (and biggest) and install.
After installation, open device manager and find the missing drives. Install them all and then then launch Windows update.