Toraricky: Thank you for your help.Now,let's see:
-I've tried to run the DirectX web Installer,but it says I already have all the files so it aborts the installation,so I think this isn't the problem;
-Graphic drivers are up to date;
-As about the temperature,I recognize this might the problem; anyway,when I close the game,my system runs just fine and when I reopen Driftmoon I can play it for some time before running in this same problem;
-I checked my disk and it's damaged in a sector.
As I said,my computer is not in the best conditions,but I found it strange that the game runs perfectly fine at first and then starts act strangely.Even "heavier" games don't give me this kind of problem.
I just wanted to check if anyone had the same problem.Obviously,if I'm the first to experience this, it's probably my computer's fault.
I'll try the Event viewer and the fps test that ville suggested and I'll let you know.Thanks again for your kindness.
Aside from this little problem,I am having a blast with Driftmoon! :D