Laptop won't power on

I posted a month ago about our laptop not starting up. It would power on then not start Windows. Well it improved somewhat for a while--I think it was a heat issue.

Now, however, it suddenly went off the other night and when my daughter tried to power back on, the all the blue lights on the "dashboard" would come on for a second, but then black out.

What does it mean when it won't even stay on? This is a HP DV9700 (Vista). Thank you!

 

I tried taking out the battery (which is basically useless anyway) and discharging by holding down the power button for over 30 seconds. Then plugging back in (without battery) and pressing power button again. No change. It still flashes the blue lights for a second then blacks out. If I hold down the power button, it just flashes on then off, on then off.

 

I also tried something else I read somewhere: pressing the power key and F4 ...did not work either.

 

This is also very much a sign of a blocked fan filter- the immediate shut off and restart shut off can often be caused by bad air flow.
I will try to upload a picture of a Toshiba fan with blockage that I took when dismantling one-as an example.
The oven trick , incidental, I have tried, and succeeded with 2 out of 4 laptops-
I found the oven setting at 200 and 8 minutes seemed to work.
I also used preformed standoffs in silver foil to raise the motherboard so that heat would not affect the other parts through too much contact. There are plenty of videos on youtube showing various methods, too.