I think you may be asking too much from your PC's resources. I don't mean to be disparaging but the hardware is rather low-end by current standards. As you said there were no errors from the sim to show why it was exiting, however the log shows a severe shortage of VRAM being made available to the sim by Windows. There are both extra plugins (SayIntentions, etc.), and extra scenery being loaded. Also, with this little VRAM, running any applications outside the sim is going to starve it of resources, even a web browser, voice chat, etc.
Can you please try to:
Remove all third party plugins, except Gizmo64
Remove all third party scenery, including AutoOrtho
Exit any non-sim processes, including background utilities, web browsers, etc., that aren't critical
If there's still a crash, upload the Log.txt again.
Thanks.