I have a pristine MacBook Pro mid 2007 15” A1226 2.40ghz with NVIDIA GeForce 8600M GT 256 MB. I hear a chime but no video,...

I would return it to Apple, then maybe you could downgrade to the MacBook Pro early 2008. Those are much better computers, and can run the latest Mac OS with a patcher. Hope that helps,

That’s too bad, There is not much you can do to fix it your pc, but your could try a factory reinstall of the os. Sorry,

Yes its possible your pram battery failed, also make sure your ram you put in was compatible( 667mhz ddr2 pc 5300 or 667 MHz DDR2 SDRAM). Try a pram reset or smc to see if it comes back on. Hope it works,

I say it looks like either your graphics card is bad or the connections in the screen may be loose or need to be replaced. Or try and see if you can boot in safe mode by restarting then immediately press and hold the Shift key as your Mac starts up, then release the key when you see the login screen. if your tech savvy you could take it apart and see if the cables are loose or damaged, if safe mode does not fix anything. Hope that helps

there is a small issue with mid 2012 retina, sounds like graphics card problem. but see if you disconnected any cables

the ram is solderd in place. sorry