New motherboard and CPU for Dell D620 and same no POST condition prevails

I've had an old dell d620 laptop for less than a year. Needed a reflow for the typical nvidia gpu issue. I fixed the same thing in a hp pavillion tx1000 with no problem, but mine refused to give any display, but the hdd and fan came on, however the bootup lights came on but turned off after 5 seconds.
I bought used/refurbed cpu and motherboard, and same condition prevails, only now there's no hdd, fan, or any other activity.
Before anyone asks, yes, I'm sure the cmos battery, psu and cable and battery are okay. I've done all the fn and function key tests, and the power button for a minute tests. I've seen many such complaints and advice, but nothing worked.
I did see one mention that there is a button that the lid depresses when closed, and that this may be stuck in the closed position, but there was no description of where it could be located. There was a mention of a 'magnetic strip' that made the contact, but I couldn't find that either. Thanks in advance for any expert info.


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If there is a lid closed switch it will be near one of the cover hinges. Will an external monitor show any image?
No. You see it doesn't stay on long enough to show up in any screen. Something forces it to shut down before it can even power up the post. I've taken this thing apart so many times, down to the last screw and plug, but I cannot see any sign of anything remotely responsible for registering the closed top. If indeed it is a magnetic strip, I would not expect to find such a switch, you see, just like a fridge door.