Dell 1555 Not Starting Up

I have a Dell Studio 1555 Laptop. It has been more than 5 years old, yet it worked excellently till last week. Now the laptop has got switched off, and it never gets switched on. I have done some experiments and following are the results.

1. Observation: When laptop switch is pressed ON, I can see the side LED light getting on, hard disk starts to spin, DVD drive tries to rotate, but after that both hard disk and CD drive stops. But LED keeps being ON. No boot screen in all the cases. FAN doesnot rotate.

2. Experiment 1: I tried to remove the residual capacitance in the mother board and try to start-up. But same observation as point 1.. 

3. Experiment 2: I have opened up the laptop, seen that there was so much dust on the FAN outlet and all. Cleaned up everything. Added new Heat sink paste. Re-run the system. But when I try to switch on same observation as point 1

4. Experiment 3: I tried to start the Laptop now, without keeping any of the RAM modules. It is normally seen, if we switch ON laptop without RAM, it will continously BEEP. But in this laptop, there was no BEEP sound. Also switch on LED light getting on, hard disk starts to spin, DVD drive tries to rotate in this case also.

Please help me to resolve this issue.

With Regards

Arun