Question : Problem: HP Laptop randomly boots with hw change

I'm working on a customer laptop that is a HP dv6000 laptop with 160 gb hard disk, wireless internal network, 1gb memory and windows vista home premium.  

The customer reinstalled vista from the disks (I assume) and after the install was complete, the machine would come on like it was booting but nothing showed on the screen... the monitor will not even light up.  

After I got it, I played around with it and removed one 512mb memory stick and it posted that the memory size had changed, I think.  Either way it posted.  I reset the bios to default and tried to boot it again and it just boots.. nothing on the monitor, not even a light, and then after 15-20 seconds, all the lights on the dash go off and come back on, the dvd rom spins up like it is trying to boot from the disk but still nothing...  It just keeps looping.  

I removed the battery, the cmos battery, the memory and the hard disk and let it sit for a while and then put in a bootable cd rom, and with NO hard disk installed it booted to the bios and the cd rom so I tried to reboot it and still the same looping reboot with nothing on the monitor.

I thought it might be the hard disk (over the phone) and once I got it here, I couldn't pinpoint it since I can only get to post once every three days of trying.  I'm assuming there's something else wrong since I can intermittently get it to post.  Does anyone have any suggestions, or is there some FUNCTION keys that I can use to get this thing to come on at least a little more predictably?   I am reluctant to disassemble the machine if I don't know what the problem is for sure.  Maybe a video problem?  I'm completely lost on this one.

The customer gave a poor explanation over the phone which is why I assumed it was a failing hard disk, but it won't even post most of the time so I'm not so sure the hd is defective.  It powers on every time but if it doesn't post, it is an infinite loop of lights on.... 20 seconds.. flash off and back on for another 20 seconds.  Only when there's a hardware change will it think about posting and it won't post anymore after I change memory sizes.  I left the batteries out over the weekend and holiday, and it booted on the first try with no hard disk and booted right up to the FBI Tools CD Rom, but then nothing after a reboot again. and again.

Any information would be greatly appreciated.

Answer : Problem: HP Laptop randomly boots with hw change

No problem at all...

This is what i believe you are looking at... Either a BIOS EEPROM issue or a Northbridge Chipset.
Either way its going to require a mainboard replacment...