I recently installed a new SSD on my 2009 MacBook and it ran fine for less than a day. However, it stopped recognising the keyboard and trackpad. 

As a workaround I tried using an external keyboard and a Bluetooth mouse but now it won't even turn on. 

I don't know if the power button is faulty or not, but I know the battery is definitely charged. 

I tried taking out each of the RAM modules but that made no difference, so either they're both fried or this isn't the problem. I also tried using the SSD/HDD but it still won't turn on. Even the white light that turns on at start up or during sleep won't turn on. Absolutely nothing.

How can I troubleshoot this further? 

Edit: After it failed to detect the keyboard/track pad, I did put the old Hdd back in. So when it stopped turning on at all, it had the original hdd in it. 

Also important : I had to reset the date (back to 2015) in order to be able to install El Capitan. Otherwise, it showed the error, 'this file can't be verified and may have been corrupted or tampered with'