Have been given a few discarded office machines, various HP machines, one was dinged up pretty bad but I was able to use some parts for a less dinged up machine of the same type so i have a working i7 3770 machine with 16GB RAM which is pretty nice, it's a HP Elite 7300/7500 machine, the dinged up one was also a Elite 7300/7500 but it was an i5 machine, I of course saved the mainboard PSU and so on.
Ar first the i7 didn't want to boot up at all, couldn't get into the BIOS either seemed to be a bit of a dud but then I discovered that there was still a drive inside, an old SSD and that was the culprit, it was deader than dead and it screwed up the poor old machine, it could detect something but not what it was so it went into a little meltdown.
Removed the SSD and after that it was pretty happy, gave it a good clean and a HDD that I had lying around, might go for a Linux Distro or maybe even Windows 8.1 since the machine has a BIOS code for that one, no need to reg etc..
Another machine I got is a scrathed up HP Pro 3500, I have a much nicer almost undamaged one so I'll use this one for spare parts as well, these are also i5 Ivy Bridge, think it was a 3740 so quad core, pretty nice though.
last but not least two Pavilion 500 machines, both i7 4790 Haswell so quad core with HT, they both are identical and have a graphics card, a itty bitty Geforce GT 530 OEM which is okay at projecting an image on screen, could maybe run a few old games but it's rather slow.. I'll keep one, the other one I'll donate to a friend, they both need a cleanup and then they'll be good to go when I find some storage for them that is, only one machine had a drive inside which was that dead SSD..
I like messing with old stuff.
*edit*
Pavilions are weird, well these older ones, their UEFI BIOS is a bit basic so it won't boot from USB stick (non UEFI) when compatibility mode is off and the system drive (SATA SSD) won't boot when it's on.. took me a while to figure that out, so compatibility mode on, install Linux Mint 22.0, reboot, go to BIOS turn off compatibility mode and the machine boots from the SSD, bit of a hassle but it works pretty well.