disconnecting things won't make it work... what did you disconnect?
the suggestion was to use a voltmeter to ensure that your +12VDC accessory leads are hot when the ignition is on.
if you had a code reader, you could check for faults on the stereo bus.
you can check in the driver and passenger front door sills for corrosion and damaged wires, water likes to get in there and corrode some of the sloppy splices.
another common issue is windshield leaks getting water into the stereo causing inoperability of the power button/volume knob
2003 Disco 2 SE7 - going to be buried in it
2006 RR Sport HSE - project
1997 Disco SE - SOLD
2003 Disco 2 SE7 - SOLD
1995 Disco SE - SOLD
2001 Disco 2 SE - SOLD
Foxwell NT510, Nanocom EVO