Notebook starts to boot then shuts down and repeats the cycle

When I try to turn on my notebook the key board lights up, it starts to boot then stops, shuts down and repeats the cycle. The screen does not come up during all of this. The cycle is about tree to four seconds long. It has been suggested that the power supply might be bad. What do you think? Also I am having some trouble getting this thing apart to inspect for loose connections. How do I open this sucker up ? Thank you for any help you can give me! This is a HP Pavilion ze 4400 notebook.
Does this happen if you start the laptop on the battery power, without power supply plugged in? If yes, then most likely it’s not the power supply problem.
First of all I would check the memory. Try reseating the memory module, make sure the contacts on the module are clean. Try moving it from one slot to another. If reseating will not help, find a known good memory stick and test the laptop again. Try starting the laptop without the hard drive. Sometimes a failed hard drive can halt entire system.
Finally, minimize the laptop as much as you can. Check all connections. Remove all devices and leave only three main parts: motherboard, processor and memory. Test the laptop with an external monitor. If you still experience the same problem most likely you have a failed motherboard.
The maintenance and service guide for HP Pavilion ze4400 has step by step disassembly instructions. Take it apart at your own risk.