Windows 7 ?

You would need to buy a fresh, OEM installation of Windows 7. You cannot use an upgrade disc, because you are not upgrading. Go to Microsoft's website (Microsoft.com), and search on their website for Windows 7 new installation. It won't be inexpensive, but if that's really what you want to do, you may have to put out the big bucks. (Sorry, I don't know how much it will cost.)

It is possible for some system to be upgraded to 7. People are going to tell you it can't be done or the drivers are not available. That is all a bunch of Bull manure spread by the people who make a profit off spyware and love the government knowing what you do on a daily basis. They are truly in love with Windows 10 and the profits it is going to put in their pockets. They are also posting a lot of false info on how to do this so it wont work for you. There are those who do not want you to do this so BE WARNED.

If your current system came with UEFI the install disc for Windows 7, which is intended for a BIOS system, will only boot so far and just stop. To fix that, you will need to build a UEFI boot thumb drive. To do this you will need a .iso copy of Windows 7, a good product key, a 8GB thumb drive, a program called Rufus, and the DRIVERS for the system you are going to install 7 on. Finding the Windows 7 drivers is not that hard for most systems. You will need to find the chipset, GPU, LAN,WiFi, and audio drivers. If it came with a SD card reader or finger print reader you will need them to. Post make and model and I'll check if they are available.

Once you have the .iso file then you need to download Rufus. You can find it here.

http://rufus.akeo.ie/

When you run it to make the bootable thumb drive, you're going to see this screen.

http://rufus.akeo.ie/pics/rufus_en.png

Follow these instruction for making the thumb drive.

http://www.eightforums.com/tutorials/15458-uefi-bo...

Once you have the thumb drive made then follow these instructions.

http://www.sevenforums.com/tutorials/186875-uefi-u...

Before doing any of this you should make an image of your hard drive just in case you run into problems.

If you do not have imaging software use Clonezilla. You will need to download Rufus USB installer. You need to read the instruction carefully and know a little about Linux to use this. There can be dragons present if you do not understand what your doing. I make no guarantees.

https://rufus.akeo.ie/

You need to download the ISO alternative version of Clonezilla. It is written to run on UEFI systems.

http://clonezilla.org/downloads/download.php?branc...

When you run Rufus it will ask you what distro you want to use, select at the bottom iso image. Then browse to where you have Clonezilla on your drive and choose as the image you want to use.

https://rufus.akeo.ie/pics/rufus_en.png

Once you have the thumb drive made you can boot your desktop using a USB port and run Clonezilla. Just follow the instruction in the link below and you will have an image of your drive. If you use a external hard drive to store the image the process goes pretty fast.

This link is for step by step instructions for Clonezilla

http://clonezilla.org/show-live-doc-content.php?to...

Drivers. The problem is drivers which are programs that translate hardware to OS. If you have a newer GPU or motherboard or other device in the computer that 7 has no drivers for, you will lose efficiency. The computer will not perform well.