2002 Chevy Silverado electrical problem (major)

My boyfriend has a 2000 Silverado that all of a sudden lost it's headlights,
interior lights, the power lock button turns on the dome light and the cargo
light button has to be on or the dome light won't come on. And now if you
hit the lock button it turns on the interior lights. Have checked all the fuses
they're good, put a new light switch in solved nothing.