HP Pavilion dv9000 laptop computer will not stay powered on and boot up. The Power on and RAM light is lit but the HDD indicator blinks twice and shuts off after 45 seconds. Then the laptop resets and attempts to power up again, ending with the same results.

Restart the notebook, press F10 and check if you see the BIOS screen or not.
If you see the BIOS screen and if the notebook does not restart in BIOS then this could not be a hardware issue.
But if you do not see the BIOS screen, then perform the steps below :
1. Disconnect the ac adapter and remove the battery from the notebook.
2. press and hold the power button for 30 seconds
3. replace the battery and connect the ac adapter
4. turn On the notebook and check
If the issue persists then remove and replace the memory modules of the notebook and check it.
If the issue still persists then it could be a hardware issue and your notebook needs to be serviced.