1) If the old PC is dead but the old hard drive is ok just copy the old hard drive contents to new PC with something like linked below.

2) If old hard drive is clicking or otherwise appears dead then try the freezer trick people mentioning. I've had mixed success with this.

3) If you need to run programs from the old PC then it gets complicated but it can be done. Either try to fix the old PC but that may be hard if major component (like motherboard) is toast. Another option is create a virtual system from old PC's hard drive https://www.stefanobordoni.cloud/virtualizing-an-old-broken-pc/