I was working on a laptop and shut it down, later I powered it up and the lights came on but the screen remains blank. Doesn't even boot POST. I've narrowed it down to either the Hdd or the memory that's causing this, but no way to know for sure as i don't have the tools needed to do so. I've tried removing the Hdd and Memory and then replacing both memory modules and booting. The pc boots into POST. Put the Hdd in, restart, and windows boots up! Restart with everything in and the whole $#!% starts again. I've still gotta try using 1 memory module at a time to see if this helps. I'll post update as necessary

HDD won't prevent POST.

Your approach is sound and on what you've said so far, I'd suspect memory.

If I've understood you correctly, replaced (different) RAM works OK, original RAM doesn't. Is that what you meant?

Not really, I'm using the original memory still, but i 'm trying them in either slot to see which one will continually allow me to boot up consistently. As i don't have the much needed additional H/ware on hand, i've got to make the best out of what i do have for the time being.