Still happened although less frequent, recently upgraded to 13.10 with nVidia 331.13 and it started to happen again in the same frequency as from the beginning.
Will contact Dell now since after some investigation this laptop seems to be prone to GPU failure and since non of my other PC's, who all have nVidia hardware, are affected, it has to be a hardware issue.
Still happened although less frequent, recently upgraded to 13.10 with nVidia 331.13 and it started to happen again in the same frequency as from the beginning.
Will contact Dell now since after some investigation this laptop seems to be prone to GPU failure and since non of my other PC's, who all have nVidia hardware, are affected, it has to be a hardware issue.