MacBook Pro won't charge/boot after upgrades/repair

My Macbook Pro 15" (MacBookPro1,2) 2006, OS-X 10.6.8 having been stored for many years, was working perfectly a few weeks ago (put in a new battery). I decided to clean her up and do some maintenance..

Thanks to all of you at iFixit, I replaced the thermal paste, upgraded the RAM to 6 GB (HT OWC) and installed a SSD (again, HT OWC). (Before anyone chides me, in all of my reading I never saw the admonition that you should do one thing at a time. I thought I was being careful by only opening up the machine once to do all three.)

Excited to see my "new" Mac in operation, I was dismayed when my MagSafe showed a flickering light. I did everything the forums suggested. I took my machine apart again to check connections. I re-installed the old hard drive, and finally went to an Apple store, where the verdict was "need a new left I/O board.

Bought a used board from PowerBook Medic, installed it, same problem.

Went to a different Apple Store and they gave the same verdict.

My question to you all is: Shall I try ANOTHER I/O board (this time from iFixit) for more $$, OR do you think that despite all my care, I could have flexed the logic board when I changed the thermal paste and broken a connection (or several)?

I can replace this machine with a virtually unused identical model for $100.

I am someone who has always had Macs, in the last decade has learned to replace RAM & clean the insides, and recently learned that I could do more to make my machines work longer.

Many thanks to any who have thoughts, advice, answers.