Sounds very similar to me.

Your mention of the offline gaming PC just because you had upgrade leftovers is exactly why I also have some of my machines. The one I mentioned not switching on for over a year was actually built from components left over from a dead PC. The motherboard and PSU failed so I decided it was time to build a new PC. But what do to with the CPU, ram and other components from the dead one? Easy, buy a new case, new PSU, second hand compatible motherboard from ebay and build another system! But there is the issue. I built it, installed and got everything running nicely in XP and then disconnected it and put it in the cupboard, not to be used until now.

I also have a SFF system that I used to use as a file and p2p system but it started to become unstable so I pulled the HD and DVD writer from it and put those in another PC and now use that instead. The SFF PC is now just sitting in it's original box in the cupboard too. I really should see if I can get it working correctly again and then sell that.