X-Plane tends to get a little more powerful and demanding on systems every time it gets a major update. Our minimum system requirements for the most recent version of X-Plane 10 (10.51) actually list a video card with 1 GB of VRAM, while you list only 512 mb in your specs, so your graphics card may not be able to handle the rendering settings.
Check the X-Plane manual for more troubleshooting tips, but you might start with safe mode to see if you can turn the rendering options down to minimums and potentially get flying again.