I just went through a similar thing with my compaq/HP nc6000. It was working fine. Took it out to collect some data, shut it down and brought it home and nothing. So, I used my wifes laptop and found this site. I found a thread where someone suggested removing the battery, and the power cord of course. Then holding the laptop upside down while depressing the power button for at least 30 seconds. Then put the battery in and press the power button.
I thought it sounded ridiculous, for real. I called a techy type person I know. He figured it was fried. So, I did as the thread suggested and when I put the battery in, the yellow light on the front flashed once, I hit the power button and she booted right up. I'm on it right now.
I've not researched why or how it worked, but I'm here to tell you, it did.