Reviving an old pc

If it is a regular width PC case. Not a narrow SFF one. Then it should be fine.

The build would be:
- Case: GTR Case
- Motherboard: Asus H61m-A
- CPU: Core i3-2120
- RAM: 2x4GB or 1x4GB + 1x2GB (I don't know how the Lenovo is paired)
- PSU: Cooler Master 430 Silent Pro (I can't find this model)
- GPU: GeForce GTX 750 Ti
- HDD: 1TB Unknown brand
- Optical: DVD-R/W (I assume this is in the Lenovo right now)

This should work well enough for simpler new games and older titles. I couldn’t see upgrading the GPU without upgrading the CPU. At the most I’d pair it with a GTX 1050 Ti. Lesser cards wouldn’t be worth the expense. As the gains are too minor.

OS: I’d install Windows 10. As MS does not require you to enter a product key nor activate it. If your friend can live without the Personalization pane in Settings and a small watermark on the desktop. That saves about $100. As MS allows this. There is no reason not to do so. As far as I have read. There are no other issues and you can still change the desktop background using options other than the Personalization pane. MS even provides the ISO and tool for making an installation disc.

Upgrades: You can pick up a used i5-2500 or i5-3550 for about $50 on eBay. There is absolutely no reason not to do so. CPUs have an extremely low failure rate. Odds are very high that if it works when you get it. It will still work 10 years from now. If you bought it new you might have an extra 2% chance of it holding up that long before failure. Don’t forget to update the BIOS first.

Just buy from a seller in your country. So, you have less return hassle in case they sell you a bum unit (which isn’t likely from a good seller). You have eBay and PayPal buyer protections as well. Then sell your i3-2120 for $15 to $20.

Once you have a cheap CPU upgrade. You can look at better video cards. I’d look at upgrading the CPU first. Although it won’t make much difference with the types of games which run on the 750 Ti. It will provide enough processing power to pair with a GTX 1060/Rx 480/Rx580 down the road. In the long run it will be cheaper than upgrading the GPU twice (GPU then CPU then GPU).