2000 Ford Focus • 100,100 miles

The car was running fine with no warning signs showing I parked it up and went to start it again a few hours later but it had no power I thought I might have left the lights on and the battery had drained so I got a friend to come jump start me but as soon as the leads were taken off it died again so we tried changing the battery but still not enough power to start it up any ideas on what it could be?
November 7, 2013.

Check to make sure power is going throught eh cbles to battery junction box, then check fuses there and ignition relay and power relay. Switch with a like realy and see if car will run. Pay attention to fuse 8 in batt junction box. It cold be a bad ignition switch although I doubt it.

Nov 7, 2013.