i are spectre

Hello to all, this is my first post and I can't seem to find a search function (yet). I can't seem to get my 4WD working anymore, it did but suddenly when I press the button in nuetral the light doesnt come on nor does it engage although it did work before. There's 150k miles on it but it runs good except for a new EGR celenoid supposedly it needs. Any idea why this would just go out? Is it a simple fuse or a major problem, where should I take it in to to get it fixed, estimated cost? Thanks, seafoam rocks too...