Help needed Laptop not booting

[harmeet_randhawa5]

I have a Samsung NP550P5C-S06IN laptop. i5 3230M, 650M, 8GB ram, 840Evo SSD. When I press the power button the fan ramps up and just power light glows. No hard drive light, no post, and when I connect charger and wait for 15-20 minutes even if the battery is charged, It turns on normally. The battery is normal. Battery life is also normal. I just cant shut down. If I shut down and leave it plugged in then it can boot. But when its not plugged in for a few hours it wont boot. I replaced RAM and I cant think of anything else that can be wrong. I can restart it normally but just cant shut down and keep it unplugged for a few hours. This is strange and I cant think of any solution. And replacement motherboard is unavailable due to the age of the laptop. I replaced the bios battery also. How can I fix it? Please help.

[Uptivuptiz]

Have you thought about replacing the battery?  

[harmeet_randhawa5]

Actually not because I dont think replacing the battery can help because its not a battery issue