I purchased my first computer in 1985, and I've been taking them apart and putting them back together ever since. I started out before all the nice graphical interface stuff with just DOS and a 286 processor, which means I know stuff about Windows operating systems and how computers are put together than most people these days never bother to learn. I know what makes them tick!
Honestly, a lot of broken computers should be retired. If you have a computer before Windows XP … it should definitely be permanently retired. Windows XP computers … maybe. Microsoft has stopped supporting XP, but if the computer is nice and it has the CoA, it might be worth a small investment to get it up and running. Vista … well, it's not the most stable operating system, but again, if you have the CoA, probably worth a small investment to bring it back to life. Anything Windows 7 or 8 … those computers should be working.
So bring those old carcasses to me! Any dead Windows computer with a valid CoA and no broken or missing hardware, I will restore your operating system for a flat fee of $50. I will back up your data onto a thumb drive or SD card for $10 (assuming it hasn't been encrypted or otherwise destroyed). And if the computer isn't completely dead but unable to connect to the internet because of infection by malware, I will clean off the malware for you (by hand … not using some worthless software) for $35 … after assessing whether it can be done.
Finally, if you are just doing spring cleaning and want to get rid of the old computer, I will buy broken computers if I think they are worth fixing.