Doesn't power on - blue LED blinks every 5 seconds

Do try these following steps that may help (Ignore the ones that you have already tried).

- Do a hard reset first, remove the battery and AC adapter then press and hold the power button for 20 seconds and try booting it up.

- If this will not work, connect an external monitor while the laptops is on. If you'll get a display from it press the Windows key + P at the same time and select Disconnect Projector or Display Only and press Enter, see if you'll get the display back onto the built in display.

- Next to try is to reseat the RAM, take them all off for couple of seconds then put them back in making sure that they are seated properly into each slot.

- Another troubleshooting step you may want to do is to try another AC adapter because it may just be a case of a bad AC adapter.

- If all these will not work that means it's a problem with the motherboard then.

Or you can check out another ifixit thread of the same problem at: Power LED blinks blue 5 time ..