Does the sleep LED ever come on, even briefly?
To make sure, remove the battery, unplug the magsafe adapter (so no power attached)
Press and hold the power button for 5 seconds, then release.
Then, insert the main battery AND connect the magsafe adapter.
Press and release the power button. IMMEDIATELY press and hold the left Option-Command-P-R.
You SHOULD hear a boot chime within a few seconds, but continue to hold the same 4 keys, while watching for the sleep LED, or ANY other response, such as a boot chime. You may hear the internal optical drive reset (a faint whirring)
Keep holding the same 4 keys. That drive reset should happen every few seconds while you hold the keys. You SHOULD also see the screen flash on, usually going bright, until the reset happens again while you continue to hold those 4 keys.
If NOTHING interesting happens, just continue to hold those keys. Waiting a full minute should be long enough for some kind of reset to be successful.
Release the keys. Press and hold the power button for about 5 seconds, then release.
Finally, press and release the power button once more, and give it 15 or 20 seconds to do something
You SHOULD see the sleep LED (in the display latch button) come on without flashing, but steady.
After a few seconds (on a working system) the screen backlight should come on, and the sleep LED should turn off at that same time.
If nothing, try removing the internal hard drive, and see if that changes the boot process (what you have now is similar to what might happen when the hard drive has stopped working. Maybe the long storage time on your MBPro has caused the hard drive to fail now)