HP6730s won't start up

I have HP6730s, which won't start up .... When I plug in the power cable and press the button the computer starts, it seems that it reads the CD driver, the WiFi light is ON, I can hear the Fan working, but the Screen is black and Hard Drive seems not loading.
Sometimes during start up the Caps Lock blinks periodically, and other times it doesnt.
I have changed the memory stick, HD from other HP6730 but without any luck.
What else should I check, what seems to be the problem.

[Gonzo]

I Think there is some issue with your Graphic card because of which you are facing such kind of issue, then that case i would suggest you to show it some engineer he will find out the exact issue at the same time check out below links for more solutions

ThinkPad T400 laptop won't boot into windows
Laptop won't boot

Thanks for the reply,

I've read the threads you mentioned.... But my problem is slightly different.... My Screen is completely blank .... I cant even boot to the Bios

[deoWo]

Hello there, I guess that the problem that you are facing with your system, that is the HP6730s won't start up may be because there is some problem with the OS itself. It also seems that there may be some error with the hardware too. So, as suggested in the above post, a computer engineer can help to fix it out.