Whenever I try to upload my video to YouTube or render my videos, it will start, then eventually shut my computer down after a few minutes. Sometimes it is almost complete when it does it which is a real pain in the ass because of all the time it takes to wait for it.
I had a similar problem with this and another NLE. Turns out my grease on my CPU had dried and it was shutting down due to heat.
Download a free program called CPU Thermometer and you can see if your particular CPU is running hot. If you have an AMD CPU you can get their AMD Overdrive software free and it will tell you lots about your system. You may have to google your CPU to see what the safe temperatures are. If you are running hot you may need an after market cooler.