Why won't my MacBook turn on?

Hi!

I know almost nothing of mac repair but am trying to familiarize myself with it in the hope that I can fix my ancient (2006) model MacBook.

My computer will no longer turn on. No reaction at all when I hit the power button. When it is plugged in, the adapter lights up orange or green as normal. The battery (not original nor mac but I have been using it for 6 months or so) appears to be charging, all lights lit when I hit the test button if I leave it plugged in a while. I have done PMU & PRAM resets, and took it to the Apple Store (where they did the same thing, then told me it was too old and they didn't have parts for the machine anymore). It does not even turn on when there is no battery attached.

In the weeks leading up to my mac's surprising death, the delete, escape, & eject keys stopped working. I did not spill anything on it, and I don't generally leave it plugged in so I doubt it was a power surge. I also had to wiggle the adapter in the magsafe to get it to charge (still need to do so to get the light to turn orange). But it does appear to be charging, so I don't think it's a magsafe problem. At the same time I replaced the battery (again, about 6 months ago) I also upgraded to a gig of ram (diy job, not actual apple RAM but compatible, Kingston). The machine was functioning well after that upgrade.

Any advice would be appreciated. I don't even know where to start... but the detailed manuals are giving me (perhaps unfounded) confidence that I can at least try to fix it.