Why would someone hack my old PC?

There is potentially a lot of useful / sellable info on that old PC that you haven’t used in a while.

What your old hacked PC can be used for by the “bad guys”

This is from https://krebsonsecurity.com/2012/10/the-scrap-value-of-a-hacked-pc-revisited/

There’s a lot of bad actors online, but there are indeed things you can do to be safer. Watch the tech site for more articles, coming soon.