While running FSX, my monitor went black and my PC rebooted with no video. I had to do a hard shutoff of the PC and it came back on OK then. What could cause this?

An overheating video card might cause this.I'd recommend clearing the dust bunnies first, and then opening up your chassis and taking a peek inside to ensure your cooling channels are clear of debris.Whenever something like that happens, it is usually a precursor to something worse about to happen. I'd also make sure any irreplaceable data on my hard disk drive was backed up.Do you have a spare video card lying about (perhaps a previous one) that could be used in a pinch. If so, I'd find it and keep it near the box.