I have a very simple but frustrating problem. I planned to replace a light fixture with a fan and light fixture. Everything was working fine - 1 switch to an overhead electric box. I removed the light - installed the fan - nothing. I have checked the circuit top to bottom - I am hot at the switch, hot at the wire nut splitting the hot line, hot at the overhead box UNTIL I hook anything to it - then all is dead. Why would power die when a fixture is hooked to the circuit? I even tried putting the old working fixture back on - now it is dead too! HELP!