[KISS]

Yipes! To me that looks like an inferior fine drywall screw.

Compare to this one:

#6 x 1-1/4" Drywall Screws, Coarse Thread for Wood Studs, Drywall Screws, Screws, Fasteners - McFeely's

Note how your's looks fatter at the end and has a fine thread. It's also full-threaded which would mess up hold ing power a little.

Combine that scew with some non-dry lumber and, I believe, you'll have just this mess.

What about it BB?

[homedoctor]

Even if the cracks are in the wood trim (base where the wall meets the floor, casing when around a door or window, chair rail when part way up a wall to protect the wall from chairs scooting back, and crown where the wall meets the ceiling) it could still be due to the house settling. So far what you've described seems minor - no windows shattering, no doors scraping the jamb, no walls falling apart. As I'd mentioned, the house may settle some more but I'm guessing not much. Tighten up the screws or add a new one above or below it. On the lid try going an inch or two one way. If you do not hit wood then the joists run the other way and you have (only) one extra hole to fill - not a big penalty when you've so many already.

Someone I know tried a trick with nails that may or may not work with screws: He used a credit card that he was going to throw away - real plastic but otherwise useless. He placed the card over the pop so that the numbers were not on the pop then bapped it with a hammer. With a nail, it puts it back without damage to the surface 'cause the plastic card spreads the blow just enough. I've used a hammer to tap in screws (before using joint compound) but they take a bit more force so this may not work for you. You've not much to loose trying it... If you do, please let me know how it turns out.

[homedoctor]

... And KISS, you're right. I could not see the pic so didn't see the screw, but the fine thread screws are for metal studs and are a poor hold in wood - too easily strip the hole they make when screwed in, especially in wet wood.