Hi MacBook pro 2012 problems

Hey all ,

my MacBook pro 2012 started playing up last week just went off while watching a dvd and wouldn't boot only got to loading screen and turned off again won't enter safe mode unless I constantly hold the shift key even after start up but if released the Mac switches off, there was no recovery hd on it. Then it started to act up on the power on / off button as in sometimes it works with battery led indicator not working, so reset the SMC and all the usual work arounds which worked for a few days but still wouldn't boot. Then led on mag stopped working and battery led indicator again So reformatted drive and installed yosmite via USB holding shift for the whole process as again if released turns off, got new 8 gb ram and installed today still no joy, also tried disconnecting battery hold power for 5 sec but still nothing

thanks in advance for all help guys

greg