Just to add to the confusion, it looks like (I am not certain) that starting
'Corel Paint Shop Pro x5' (not to the level of the older one PSP!) would also freeze my system, but only for 3 or 4 secondes. The clock is still running there, just the task bar and clic on a desk icon are stuck.

Out of subject, I would like to add that Corel was reluctant to analyse the fact that when their program starts, the Light level of the desk is increased by 5 ticks, and Nvidia panel just has to set up and down to normal level to reset the desk (Corel still running !)

Another of the Gremlins in PC ?