X51 - short freeze - rainbow pointer and crashes

Since a month my computer:

- freezes ever so often and recovers or not.

- looses dvi signal while still running

- freezes all together

- and has the pointer go rainbow color, or stay in one pointer mode or an other.

Or all of these at the same time

Did a F12 computer check all seems fine, opened and cleaned all the inside for dust, reinstalled windows and all drivers are I think up to date.

I am running out of ideas as to what to try next ?

Thanks for your help.