So a friend of mine gave me a cheap computer he made his sister years ago cheap little build for web browsing etc.. they couldn't remember the password and didn't care about anything on it so I hooked it up to my PC and formatted it all. I went into Microsoft's website and tried to use one of my "pre installed" codes from one of my other computers and it won't let me for an ISO file. I'm figuring what I could do next but looking for ideas/opinions.

Windows 10 is 5$ for an oem key on ebay

This.

I purchased a copy of Win 10 Pro OEM for 25€ just yesterday (not on ebay).
Win 7 it's too out of date...

I like windows 8 personally.. windows 10 is okay. Its preinstalled on my gaming laptop didn't have much of a choice. But thanks guys

Man Windows 8 was designed more for mobility tablets and convertible laptops. 8.1 was a sort of "fix" to make it more suitable for standard PC purposes.
Windows 10 is more similar to Windows 7 than Windows 8 is.

Just give it a try, you won't be disappointed.

Use Windows 10, if you are a student you can get it for free.

Don't be that person clinging to windows 7 like a grandma clinging to windows XP because it is safe and familiar.
The reason we live in an age of ransomware and crypto is because of morons who wouldn't keep up and Microsoft and others had to make shit work for the old ass operating systems and left gaping holes in the news as a result.

Do you need a preexisting install of windows to use the educational version of Win10 that you get for being a student?

I do not believe so, but if for someone reason you need a key, PM me

Got the problem resolved thanks to all for the advice

Did you end up reinstalling windows?