Hello and welcome to Techspot.
Four possible causes spring to mind.
1 An under powered psu.
2 Faulty ram.
3 A faulty device driver.
4 Overheating.
You can test your ram by downloading the Memtest86+ programme from
www.memtest.org.
Let the programme run for at least seven passes. If you don`t have a floppy drive, there is a pre built iso version available, that you can burn to cd, and then boot from that.
As for an under powered psu. Look
HERE at this psu wattage calculator. Remember to add a further 30% to whatever figure it says you need.
You can stop your computer from automatically rebooting when there`s an error. Right click my computer, and select properties, then the advanced tab. Under startup, and recovery, click on settings. Untick the box that says automatically restart, click ok/apply the required number of times, and reboot your system.
Now instead of your computer rebooting when there`s an error, you should receive a stop message(BSOD) telling you what caused the problem.
Pay particular attention to any drivers identified in the stop message.
A list of Windows stop messages can be found
HERE
Make sure you have all the latest drivers for your system, including the chipset drivers.
For monitoring you temps. You can either use the free Everest programme(see the link in my sig), or the Speedfan programme which you can get from
HERE
Regards Howard :wave: :wave: