I have an '89 420 SEL. Two days ago I attempted to start it and the only response I received was the fuel gage registering how much gas was in the tank. No lights (internal or external), radio, climate control, etc. worked. I wiggled the shifter and shifted into nuetral - no luck. I tried to jump the car as well. I pulled the battery and checked it - registered a good battery. After putting the battery back, it started right up. From there it ran for over fifteen minutes before I shut it off. I started it up several times after that without a problem.
The next morning it would not start. Tried the same steps as before without success. The battery and regulator brushes are recently new. Regular tuneups, fuel pump relay replaced, good ground from the engine to the body, battery terminals/ wires are in good condition and all fuses appear to be fine.
Any thoughts? I am an average DIYer so try not to get too technical with suggestions. The other problem is that I have recently moved and have not unpacked my CD's and repair manuals.

Thanks in advance for any help.