When someone makes a post like the OP and asks "Where do I start?", my first impression is to say "Call an electrician".
We know nothing of the OP's capabilities, experience or tools/testing equipment.
shakydoctor, can you tell us a bit more about this situation and your level of expertise?
Has someone wired an recepticule into a switch loop ?
bad neutral also poss'
Loose connecttion somewhere ?
Unless it's something simple like a loose wire
then it's not really something for a novice to fix.
Recomend an electricain !
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