When my old desktop gave me too many headaches, last October I bought a refurbished HP with Win 7 OS via Amazon. It cost about $200. No mouse, monitor, or keyboard because I didn't need them. It was delivered in three days, free shipping, and I don't even have Prime.
HP dc7900 SFF Desktop Core 2 Duo 3.0GHz, 4GB RAM, 500GB HDD, DVD Burner, Windows 7 Professional 64-Bit Computer
Sold by Computer Combination
Condition: Used - Very Good $198.00
I had purchased a Dell laptop with lots of bells and whistles in April of '14 with OS 8.1. I hated it from the beginning but I've been told that OS 10 is better. After ignoring the machine for 6 months, I tried again. Because of major problems with the laptop, that I spent dozens of hours unsuccessfully trying to rectify, I had to give up and call a local tech repair guy. He said he prefers Windows 7 to both 8, 8.1, and 10, and I should wait at least six months to upgrade to 10 because there are so many bugs. In addition, and this is important, Windows 10 has absolutely no security in regards to their tracking and gathering your information. Everything on your computer is accessible to them, and you give them permission just by downloading the OS. Email content, web searches, blog posts, everything. So I'm staying with 8.1 for now, and might download the classic shell, which emulates Windows 7.
http://www.classicshell.net/
The repair guy is going to clean what needs cleaning and fix what needs fixing, remove all retail security programs and install a super-duper security program -- all for $100 to $150 max. Not bad.