This is a shot in the dark, but it sounds like you have some harware that is loose, or worse, in the laptop. By worse, I would say there is the possibility of a faulty circuit inside the graphics chip which, after warming, "resits". On subsequent reboots I would guess your computer had no more problems?
If that is so, the remedy is (almost) unobtainable. To get such a chip repaired is sometimes not worth the expense on a laptop.
But, optimistically, pay heed to Salt Grass's suggestion. Try first to look in the startup tab in Msconfig and untick a few items there.