Continual screen freezes

[Crusader]

I have no problem signing on or playing, except more and more frequently the screen just freezes...no error message. When I minimize the screen and re-enlarge the screen it goes black...after about 20 secs the entire screen goes black (when playing the play screen does not fill the entire desktop). This last episode happened after about 30 min playing time in N. Karana, but this has happened in Qeynos Hills and N, Qeynos as well.
The truly disheartening aspect of this is that after an hour of combatting light and dark blue mobs, I was root rotting a Griffawn last night, the screen froze, I could still hear the audio, had to power down the computer as CTL-Alt-Del would not get me to the task manager so that I could terminate the connection. I logged on again at my bind point dead, having lost more exp than I had gained in the past hour. I hope this isn't part of the "challenging game experience" I signed up for. At this rate I will be forced to group, where going LD while in combat will not automatically result in my death.
My character is call Lcdr.