Tell me about it. I had a litter of mice up inside the wall of one of my bedrooms. I could hear them thumping around but couldn't figure out how to get rid of all of them at the same time. Then the mother got eaten by an owl or something, and after 2-3 days the litter died. And it stunk - I mean a sickly-sweet, eye-watering miasma that turned that whole room into the Amityville Horror. I've dealt with a dead mouse in the wall before - give it a few days and it will dry out. I don't know how many dead mice were in that wall but they had the collective putrifying power of an adult opossum. After a week or so, I was this close to cutting a hole in the wall and scooping them out myself. Good times...
1. If you put out traps or poison, put it along the walls. Mice tend to hug the walls when they travel (don't like being exposed on all sides).
2. If you put out a trap - and the next day the trap has been sprung, and moved a considerable distance - you need a bigger trap. True story.
3. Seal up any holes leading into the house and get rid of anything that mice might want to hide in, under or around. Time to take those old newspapers to the recycling center.
4. Get a cat. They're wired to hunt and almost always get their mouse, unless the mouse is Speedy Gonzalez or a baby kangaroo.