Compaq presario won't start?

My compaq presario c502us just went blank. With power supply plugged in and battery inserted I get a rapid flashing light on LF of case, If I push the power on button to start laptop, there is a small flashing light the comes on in the middle of the power button and it flashes for about 5 seconds and then goes off but computer does not start? I have tried to remove the back of the laptop to do some trouble shooting and have removed all the visible screws, hard drive, and memory but there seems to be a screw or ? that I cannot locate in the area of the fan that is preventing me from taking the back off? I have done some voltage checks on the power supply and the terminal block right behind the battery and I have proper voltage.[this is my daughters laptop and she said that her husband had ordered a new battery and power supply and they made no difference?
Thanks