I don't think any of these are a good-value advise. He's one from my personal experience...
The best way that I ever revived an old PC was to get an updated SSD for it, with a fresh OS. My PC was constantly out of space on the system drive, with an old Samsung 256GB SSD, and Windows accumulated too much garbage over time that was almost impossible to root out. Investing $90 into a 1TB Samsung 870 QVO, and getting fresh Windows 10 made all the difference in the world. I only wish I did it earlier.
And I got Windows 10 Pro license for $20 here - https://www.cdkeysales.com/microsoft-windows-10-pro-oem-cd-key-global.html
Sadly it looks like all the 140mm singles I thought about are discontinued, the NZXT Kraken X42 was probably the last one until it was canned. Corsair had the H90, Cooler Master had the Nepton 140XL, both of these are long gone. Unless space is a limitation I'd say a good air heat sink would be better performing at this point in time, otherwise you'll need to look into custom loops or buying a new AIO and swapping the pump/block onto your existing 140mm rad.Unfortunately, 140mm single fan water coolers are really hard to find now. Does anyone have a source on one? That system is 6 years old, and I will need to replace the cooler eventually.
Investing $90 into a 1TB Samsung 870 QVO, and getting fresh Windows 10 made all the difference in the world.
Meh, again it isn't about the PC itself but the case. If you are replacing the components but keeping the old case, these ideas can be useful.If its old its old , of course you can renew smtn but it wil not work for long or so good, so better to save money and buy better PC