System does not boot up- Acer Aspire 5500z (AS5502Z)

Hi, I have Acer Aspire 5500z (AS5502Z). When I power on - there is no boot The screen is black (and I am using external VGA monitor since the original screen got damaged). The power indicator is on. The fan is running low speed.
Since I had it for a few years was heating a lot. Lately it could power off in the middle of any process. Before it was once a week. Most lately - several times during the day.
Other history: from the beginning screen could change color periodically and then come back to normal.
I hope I can restore it with you help.
Also another question what would be the part # for the LCD panel?
Thank you