Dell XPS 15 Power up issue

I have a Dell 15 XPS L502X

Recently the power button has started giving trouble and the laptop does not turn on.

Only after many minutes of trying then it switches on.

But if I shut it down then it starts giving the same problem again.

Also the left button of track-pad has stopped working.

I have tried earlier solutions suggested like draining flea power, running only on adapter etc. but the erratic behavior of my laptop continues

Please let me know what I need to do?

- Flash my BIOS (I have flashed it once)

- Change my track power cover (contains power switch and trackpad)

- Change my motherboard

- Anything else