How do I narrow down why my laptop wont power up.

@klp5309 start with something like this

Resetting the Power Manager (SMC)

Power management is now handled by a chip called SMC (System Management Controller). Previously, it was handled by the Power Management Unit (PMU). To reset the SMC:

If the computer is on, turn it off.

Disconnect the power adapter and remove the main battery.

Hold the power button down for five seconds, then release.

Install the main battery and connect the power adapter.

Press the power button to restart the computer.

Startup

Startup Sequence

The Intel-based MacBook Pro starts up very much like the previous professional Macintosh notebook computers. If power is available to the system, after pushing the power on button the system will start to boot up.

The screen will stay dark. The sleep LED will glow solid. This will last a few seconds.

As the system boots, a power-on self test (POST) will be performed. See Error Codes listed below for failure results.

If the system is not muted, you will hear a boot beep. The backlight will turn on and the sleep LED will turn off.

The screen is gray in color. The Apple logo will appear and then the turning gear will appear.

The desktop pattern will show up, as well as the menu bar start populating.

No Power, No Video

The computer will not power on (no fan movement, hard drive spin up and display is not lit).

Remove any connected peripherals and eject any ExpressCard.

Check that the battery has enough charge to start the computer by pressing the button next to the LEDs on the battery. At least one LED must light solid (not flashing).

Connect a known-good Apple 85W Portable Power Adapter and power cord or plug to a known-good power outlet; make sure the DC plug is properly inserted. The DC plug should light up, if not, replace left I/O board. If not go to the troubleshooting, MagSafe connector.

Try powering up without the battery installed If it boots, try a known-good battery. If it does not boot, replace the battery connector cable.

Reset the power manager or SMC. See new procedures under the “Resetting the Power Manager” heading in the Hardware Troubleshooting Tools and Tips section.

Boot up the system and check the sleep indicator. If it turns on solid and turns off, the main logic board is getting power and completing the boot cycle. If no video appears, there is an issue getting video to the display, or system software is corrupted. Try booting from the Mac OS X Install DVD. If the light does not turn off, the boot cycle is not being complete. This may be caused by the hard drive not being detected by the system, system software corruption, or possibly a hardware issue.

Press Caps Lock key to see if the keycap LED comes on. If it does, hold the power button down for six seconds to shut down the computer and restart.

If it still doesn’t start, verify that the power button cable is connected properly to the top case flex cable assembly and that the flex cable is connected correctly to the logic board. If the power button is damaged or not functioning correctly, replace the top case.

Disconnect the keyboard completely. Inspect the connectors. Restart with the keyboard disconnected.

Remove any additional RAM.

Try removing the AirPort Extreme card from its socket and start the computer. If it starts, shut it down and check the flex cable connector and the connector on the logic board and replace the damaged parts.

Reseat these flex cables:

• Left I/O flex cable

• Hard drive flex cable (will boot to flashing folder if not connected or corrupt)

• Optical drive flex cable

• Trackpad flex cable

• Display LVDS cable

• Thermal sensor cables

If the computer starts up, inspect the flex cable connector and its terminal on the logic board for damage and replace the damaged parts.

Try known-good left I/O board.

Replace logic board.

Before replacing the logic board :-) let us know what you get and what you found.

Power-On Self Test (POST) Error Codes

The computer automatically performs a power-on self test when it is turned on after being fully shut down (not a restart). This section describes what to do if beeps are heard during the startup. When this occurs, the sleep LED will stay on, occasionally flashing.

MacBook Pro relies on a combination of tones and blinking sleep LEDs to display power-on self test (POST) error codes.

If the computer detects no SDRAM (Synchronous Dynamic Random Access Memory, also referred to as RAM), or the RAM installed does not meet the appropriate specifications, the screen will remain black but the power LED on the front of the computer will blink once per second to signal the error. This error condition may be due to physically damaged RAM, installing the incorrect type of RAM, or not having RAM installed.

Some RAM may appear to pass the power-on self test (POST) but still cannot be used by the operating system. In this case, the computer will display a gray screen, sound three tones and blink the power LED on the front of the computer three times, pause, and repeat the blinking until the computer is turned off.