For checking ram,use the small utility memtest which is free and let it run for 3 to 4 hours at least.If memtest does not give any error then your ram is fine.Now for your flight sim crash problem it could be due to a number of reasons including virus so first scan and remove all viruses from your pc and re install sim.Another reason could be due to card overheating so remove all covers and also check its temperature from the video card utility.