After replacing screen notebook won´t turn on


TS Rookie
Due to broken screen I have replaced it (notebook Toshiba Satellite A660-135). After having done that I tried to start the system (Windows 7 Pro). I removed the battery because it doesn´t work. I plugged the charger into the mains, the led indicator lights up. I pressed the starting button, it also turned on, the cooling fan came on, a click from the DVD/CD drive came on, too. But after about 5 seconds the notebook turned off. And it repeated again and again. I also tried to push the starting button for some 60 seconds and repeated again the starting action. Always the same result.

Previously, the laptop worked correctly when I connected it to an external monitor. Is it possible that I made a mistake while exchanging the screen? But the procedure is very simple, or is there a hidden problem? I would appreciate any tip.