1 doublecheck to see if they are putting discs in backwards
2 verify everything else works: wiimote, internal memory etc.
3 do you own call of duty:Black Ops? it is known for breaking the laser
4 ask them if they tipped it over
5 assess how old the wii is and if it was exposed to a lot a dust
6 access if the discs are smudged or scratched beyond recognition
from 1-6 you might conclude that all it needs is a cleaning kit (can be found at walmart or even hmv i think) or that warranty might cover it, either through shipping it to nintendo or deal with the in store warranty. If not you can still pay nintendo to do repairs or else much easier to find a game store in your hometown to fix it.