It's very unlikely (but still possible) that PJ64 is causing the problem because it would just give you an error message, not cause it to reboot. It's more likely caused by overheating, bad graphics drivers or dare I say it, a virus. The first thing I would do is uninstall PJ64 and reinstall it. If that doesn't work, then hopefully it's just the drivers, so try uninstalling the graphics drivers and reinstalling them. Also run a virus scan just to be sure.
