I had a similar problem with a mag 5. The housing was cracked, at the tip where the impeller meets. I had to plug it in, remove the screws, pop the cover slightly off, it'd kick on, then reinstall cover. I was about to order a new cover wait ordered a new skimmer. It's not uncommon on mag pumps. New housing is only like $5-6. Also make sure your impeller is ok, not missing an o-ring, cracked etc.