Oh, that is well structured question... =D
1. Yes, I tried blink sketch with and without motor shield
2. Yes, I load blank sketch and then during tests it was working fine for 2 hours
3. There is only 4 elements, 12V DC adapter, Arduino + Motor Shield, Motor (Motor Shield feeds Arduino)
4. Yes, motor works fine with just 12V DC adapter
5. Motor works at 4.5-15V
6. Yes, I used that source to make my first trial
Power Jumper configured to feed Arduino from Motor Shield
For more details, when I load sketch from the computer it says that it is loaded, but RX TX lamps are lighted but don't blink.
When I run program all led lamps lights and then start to fade by pulses and motor doesnt run. Arduino board heats.
It happened when I was unpluging and pluging DC adapter