Sounds like you are killing your computer (figuratively) by
demanding more of it than it is able to deliver with the resources
available. This includes RAM, free (contiguous) HDD space, graphics
card memory and bus speed, and CPU abilities.
Give the machine and yourself a break by avoiding pushing it
beyond its limits, if at all possible (I know sometimes it is not).
Full screen mode creates a very large picture (background image)
with each snapshot, and if you are using full-motion recording, it
is even worse. Add to that the resources required for narrating
audio, and you have a recipe that spells "over-demand and
under-powered".
I would take a guess that the blank screen issue is a
graphics issue, again having to do with asking more of your
computer than it is able to give you. If you are not able to
capture a smaller area, to lighten the load, and cannot avoid using
full-motion-recording (FMR), I would look at hardware acceleration
on the current set up, and perhaps a new, more capable graphics
card. Good luck! Larry