Hi!
I have gone through the same problem (on multiple games including SC2, MW2, ArmaII, etc) and i believe i am familiar with it.
Qosmio crashing during games (even freecell) with a black screen and loopy sound from the speakers. Solved only with a hard reset. Problem does not happen if you are running off the battery.
I believe i might have a solution. I have seen the problem crop up across the board on all Qosmio laptops (including my own X300) and i eventually did quite a lot of research and found out a solution.
The problem really pertains to fixing the clock frequencies between the GPU and the CPU and that caused all the problems. They apparently loose sync with each other at variable speeds due to a bug in the power management.
The detailed explanation and solution are on
http://www.fixmyqosmio.com and you can check out the writeup there.
It worked for me and it has worked for over 100 other people who have liked it and used it. !!Warning!! it is a COMMERCIAL solution (although it has a 100% refund guarantee) so dont go to the site unless you want to.
I am not soliciting for business. just letting you know that there IS a way to solve the problem and Toshiba are either not concerned or unable to solve the problem. Please dont make the mistake that i made (taking my out of warranty laptop to toshiba) and paying for servicing it.
The service center cant help as it just DOES NOT KNOW how to solve the problem. They service it and hope for the best.
Hope that was some help
LordNOD