Beware of carbon atoms with 5 bonds (AKA 'texas carbon') when you draw your mechanisms... if you find yourself with an intermediate that has one, it is undoubtedly wrong. Be especially careful with the presence of implicit hydrogens on your structures - they can't just disappear!
Babcock Hall is right - protonate the oxygen and think about what resonance forms that leads to. When you encounter a molecule like this and you don't know where to protonate, remember that the lone pairs are the most 'available' electrons for protonation, so it's more likely that these are protonated than one of the alkenes.