Víctor and frisor,
I suggest contacting your laptop manufacturer for support. They are the ones familiar with your system's compatibility and support for it.
hi again, as i read in some webs that putting two diferent size memorys together (or diferent brands) can cause problems, or even to test if it was because of an 8GB memory limit, i tried to put only the new 8GB memory alone, to see if that solve the problem, but nothing new, i had the same random shutdown/restarts, i even got one after pressing restart, with 0 aplications on and after i had reseted my notebook.
So i called the hp support team (there were some other problems too), and when i asked, he said "there shouldn´t be any problem with that ram", so my conclusion was that the memory i bought was failing, I went to where i bought to get a solution, and now they are "testing it", and im waiting.