Cristan,
We had the same problem, ours was related to (belive it or not) our image
deployment strategy in that all machines where forced to use the Standard PC
Hal and our image had every driver for every possible machine installed (by
downloading the image to every new model PC received, installing the drivers
and the uploading the image again for distribution). We now use a hardware
independant image deployment strategy which has resolved this problem so that
the computers get the right HAL and also that drivers only for the specific
motherboard model are installed.
My hardware guru tells me it was more then likely related to using a wrong
version of graphics driver for the onboard graphics chipset (especially in
the case of Intel onboard graphics chipsets), our most troublesome
motherboard model being the D915GVWB Intel Chipset (which is what we
discovered this problem on).
Hope this helps.