Hi,
Have you tried it by pressing and holding it until it turns on? Do try these troubleshooting steps as well and see if this will solve the issue or not.
- Do a hard reset first, remove the battery and AC adapter then press and hold the power button for 20 seconds then try to boot the laptop.
- Next is to test the AC adapter and see if it's supplying enough voltage or better yet try another AC adapter that has the same voltage.
- If that will not solve the problem do reseat the RAM, remove them all for couple of seconds then put them back in making sure that they are seated properly into each slot.
- If all these will not work you may need to replace the power button itself if it has been acting up for quite sometime now.