Electrical issues

I am having some electrical issues.

I am trying to replace an in-line duct fan and cant get it to power up using the electrical wire that was used before.

Its standard romex (black, white, cooper). The weird part is when I use a "sniffer" pen to test if the lines are hot the white wire comes back hot too. I have pulled the wires apart to make sure that I'm not getting a reading from the black wire.

Anyone know why this would happen or how I could fix it. It should be noted that as I was trying to hook up the new fan I accidently touched the black power wire to the J box. It made a small spark. No breakers were tripped.

Thanks

Are you sure the new fan is good?
There could be a humidistat under the floor that is not on.
There could still be a breaker that is off but does not appear to be.

A couple of things, "sniffer" pens (non contact tester) are not a definitive test as they often lie saying things are hot that are in fact not. Please use a real tester, either a multi meter or voltage meter. Read both the black and white wires to the ground wire (hopefully the ground wire is in fact grounded) if you read voltage between the white and the ground then 95% + you have a open neutral connection somewhere. Circuit breaker handles do not always move much or at all when they trip, turn off all your computers and then turn off and back on all your circuit breakers. The "small spark" when you touched the black to the box makes me wonder if the wiring is on the load side of a GFI or a Arc Fault breaker, check for GFI receptacles (the ones with the buttons) that may be tripped

inductance. Those pen testers can tell you a wire is hot when it really isn't just because it is sitting next to a live wire. I own one, but don't rely on it. You gotta make sure you are getting proper voltage. Also make sure your fan is rated 120v and not 208v. Or was your old fan 208v to begin with?

I got the same replacement fan. I'm going to check the breaker today. I hooked the fan up to an extension cord and it works.

Got it figured out. Long story short, it was some wierd wiring in the j boxes