Macbook Pro A1278 Hard Time Powering On

Good morning all. I'm working on a friends macbook pro7,1 a1278. When you power it on, most of the time the keyboard will illuminate then go out. There is no power sounds what's so ever. I find it I hold the power button down, and wait for the light again let go then click the power again it works fine. Now every so often, it will work like normal. I have replaced the battery, and have a new power unit. I also have done the SMC reset, and restored the system with a fresh install. So, I hope that someone might be able to shed some light towards the area that I am obviously missing:) Thank you for any help.