2010 13" MBP and Boot Camp/Windows 7 errors

Hi!

After a lot of searching and finding people with kinda similar problems - I havn't exactly found an answer yet, so I hope you guys can help.

I'm on my mid-2010 13" MacBook Pro, running El Capitan, (old thing, I know - but it still runs quite good) trying to install Windows 7 through Boot Camp.

I read that Boot Camp should be able to create a Windows USB install disk, but that option was not available to me - so I tried editing the info.plist file and the option came up and I ran it. Boot Camp created the USB, but when trying to install Windows I got an "Non-system disk" error. I researched further, finding that editing the info.plist file wouldn't work when trying to install Windows.

Then I used my friend's Windows computer (we do not have one ourselves) to create the USB via the Microsoft DVD USB Tool, which worked just fine. I was now in the Windows 7 install menu, and when asked to choose the partition to install Windows on, I chose the "BOOT CAMP" partition.

New error came up: "Windows cannot be installed to this disk. This computer's hardware may not support booting to this disk. Ensure that the disk's controller is enabled in the computer's BIOS menu."

And now I'm stuck! I tried to format the partition in the Windows install menu, with no luck - same error.

I read about a Windows disc being the only way to install Windows on a Mac with an optical drive, but does that have anything to do with new error (after making the install USB on a Windows computer), and what should I do from here? Have been trying to install Windows for the last week now!! (not only that of course, haha)

Thanks guys!