@Sidney Eliot Generally speaking, these shadow issues are fundamental to all renderers, not specific to Toolbag. There are some tricks that can be done in raster rendering engines to soften shadow faceting somewhat, but as you note in the last part of your post it's a problem there too. The software can only render shadows…
Ok, so I'm not a technician or whatever but in my experience - if the computer is rebooting like that then it's a hardware issue. Power supply, GPU or a mainboard that can't quite cope with the attached hardware running at full load. In your case I'd get my hands on a much much lower spec GPU first and try working your…