1998 Ford Taurus WIll not start

Electrical problem
1998 Ford Taurus 4 cyl Front Wheel Drive Automatic 109k miles

Car has been sitting for a couple of months with no previous problems. This morning the battery was dead, I replaced the battery and attempted a start, all the lights stayed on but I only heard a clicking sound. I then though that the starter and solenoid had possibly frozen. They checked good at the local auto parts store, I then inspected the wiring for corrosion. The positive cable was questionable and replaced. I then checked all the relays associated with the start system, removed, inspected and cleaned if necessary. All the lights come when the key is turned to the on position but once key is turned to start, the entire electrical system shuts down, no clicking sounds. Removing the positive cable from the battery and reinstalling resets the system. Any suggestions where I should look next?