As much FS9 is a heavy program, a hard crash is usually not at all one of its faults, at least directly. Fact is that FS9 is rather hard on the hardware and if the HW is not perfectly balanced, it gets hairy.
More probably and prosaically though it's quite easy that your CPU heat-sinker has become clogged with dust and other unpleasant materials gathered by the fan and seen that FS uses intensely the non efficiently cooled anymore CPU, this goes in overheat and makes the PC fail. First thing I suggest you to do is to buy one of those air spritz cans used often to clean the keyboard and use them on the fan and heat-sinker to clean them some. Eventually, if you have experience on this matter, you should unscrew the fan from the top of the heat-sinker and give the both of them a thorough clean-up (or make a PC technician do it for you).
Try this first and see how it goes.
PS
Welcome on the forum.
