Macbook randomly won't start

I have a white Macbook, few years old.

It was stripped down for a clean out due to the insides being all dirty. When it was put back together it all worked fine for about 2 hours until it just turned itself off!

Following this it's start up was intermittent and would usually boot absolutely fine then shut off after 30 mins or so. When it was working everything worked like a dream until it shut itself off.

Now it won't turn on at all! When you hit the power button the fan moves a fraction and the screen flickers but that is it. This happens each time you press the power button and if you hold the power button the fan just moves a tiny fraction repeatedly.

All the hardware connections have been checked so everything is connected fine inside. I'm totally confused what can be wrong with it! Any ideas?

Did you get it wet at all when cleaning? Try a pram reset or smc reset to see if that solves the issue.

Thanks for you reply. No it didn't get wet. I will try PRAM and SMC reset.