Check for GFCIs, not sure the age of your home, but lights and especially a bath fan should not be on a GFCI or you'll get nusance tripping. My parents house has the garage door opener on a GFCI circuit (very lazy electrician) and it'll trip from time to time, motors can have that effect.
Anyway, you may want to cycle all your breakers, some get older and don't always look tripped, so it's easy to think it's still on.
After the basics something has got to be causing a break in the circuit, this just takes some detective work looking for a broken component or connection. The only thing to remember is white is negative, bare is ground (green is ground but not usually used in a house), and anything else is going to be hot or a switched hot. If you can handle DC you can handle AC, just don't touch anything that you aren't positive is off, 120 stings a little.