Sounds like the dreaded Click - Click failure where a cap shorts in the control head and drops the CPU that has to communicate with the digital unit in the main unit.?
Sometimes this is an easy fix and sometimes not.?
First try cleaning the panel connectors (you may be lucky).
There are two regulators in the head that provide the +5 and 3.3 volts for the head processor.
What happens is you get the power up signal to pull in the relay and then the CPU in the main unit has a few seconds to get a serial signal from the head to turn the rest of the radio on. Without this signal from the head the relay drops out.
This is repairable and is sometimes easy and sometimes not.
Often it is a cap in the regulator circuit that has shorted and this does require some troubleshooting and can (as I have learned) relatively easy or (in my one case) impossible).
If you Google IC-7000 click - click you should get a number of hits that will guide you in your endeavors.
