We built the pc, but when we plugged it in, it won't turn on.

Any thoughts?

We took it apart and put it back together again double checking that we put everything together correctly but it just doesn't turn on

https://www.youtube.com/watch?v=ixcWCrYpw3Y

try this and let us know if its fan spins first.

Check the case pins for power btn etc

I reversed +and - once and couldn't figure out why it wouldn't power

that shouldn't matter on a power switch.

What CPU and motherboard?

Yeah

It's was the pwr led/pwr switch

Seems the power supply was bad. I tried this test and it didn't work, so I took that power supply and hooked it up to my other pc to see if it would turn on and it wouldn't so it seems the power supply was defective.

the led wont function but the switch should still work.

glad you got it fixed

No

I plugged the led ones in the pwr ones

Causing the switch to do nothing

Motherboard and CPU were bad...