Your information is completely contradicting and thus makes it impossible for us to fix your problem when we dont even have a starting point for what the problem is.
Wont Turn On - this means no lights, no sounds, no display, ZERO signs of life (just like if it had no power at all from charger or battery).
Wont POST - Lights turn on, possibly fan/hard drives spinning/making noise, if screen does come on it is black.
POSTS wont boot at all - screen comes on and you get your BIOS screen and it loops to that screen without trying to load windows
Wont Boot into OS - lights/sounds/display all working, you POST just fine, system starts to boot into windows (so you see a starting/loading windows screen), but fails.
Please tell us out of...