(Sony Vaio VPCZ13) Green power light blinks but doesn't turn on

My notebook is a VPCZ13M9E/B, that was bought on March 2011.
After using it correctly for years, suddenly doesn't turn on, either with power cord or battery. The green light just blinks one time every 3 or 4 seconds or so, like if it were trying to power itself on and powers off; then repeats forever. Keeping the power button off for a lot of time doesn't fix the issue, and doesn't either removing the battery and powering on with the power cord only. The only other light that comes on is the led that is next to the graphics slider (Speed, Stamina, AUTO), all the other lights from disk activity to keyboard backlight are completely off and the fan or screen don't turn on either.

What can be the cause?

 

Ok, just looking on the internet found and tried this solution:

my power LED green light is blinking and laptop won't start

Just removed power cord and battery, removed the two ram modules, and tried one by one, and surprise, the laptop started as usual. Then put back the two modules and voilà, worked again like if nothing happened. Very intrigued if some ram module moved or what could be the cause.

 

Loose contact, probably. One of my RAM modules failed recently, so I took the opportunity to upgrade from 4GB (2x2GB) to 8GB (2x4GB).