I have a funny custom-built PC story:
6 years ago I built a budget gaming PC for my son with help from CAG. It was the only time I ever did that and I think it worked out pretty well. I probably need to look into some upgrades but that's for another post. If I can find the specs I'll post them and see what you guys think.
So... It was in my son's room as he went through high school and community college. He's now a college junior and didn't bring it with him. He told me the hard drive was bad - making noise. I hadn't looked at it in years. My younger son took over his room and just last week wanted to get the PC working. Sure enough, it is making a horrible rattling noise. It is also dirty and dusty so I start to clean it. Then I realize something big is loose inside the case.
I opened it up and the

-ing CPU fan (the motherboard is mounted along one side, vertically) is laying down loose on the video card. The rattling noise was the fan turning on and bouncing around on the graphics card! He must have knocked it over at some point and then this started and he didn't tell me. The fan is held in by 4 pegs that snap in and it had come loose - had to have been a fall to knock them all loose.
I was able to put it back up there and now it is quiet again. After a Windows 10 upgrade (my son had wiped it clean and re-installed Windows 8 which left it without even having a network adapter driver), I was able to get it up and running for my younger son and he's happily playing Terraria, which this PC can handle just fine.
So, it ended well, but I almost wanted to drive down the freeway to where my older son lives and smack him

. Oh yeah, there was also sticky Coke residue that had leaked through the top USB/microphone ports and dripped down on top of the outer case of the DVD-ROM drive. I'm really surprised the thing worked after all that - especially with the CPU fan having been detached for so long.