Hi and welcome to Geeks to Go. Random reboots are usually caused by heat, memory, driver issues or the power supply. You need to examine each one and fix it or rule it out as the cause. Start by opening the case and checking the fans/heatsink/inside for dirt. Canned air is a good way to clean it out. Just make sure the "canned air" container remains upright as you use it. Once you know the fans are working and the computer is clean, move on to the next possible cause. Test the memory with http://www.memtest.org/
. Make sure the drivers are up to date. If you need to update the video driver, clean the existing intallation with Driver Cleaner (http://www.drivercleaner.net/
) before installing the new driver. Once all of this is done, consider the power supply as the possible cause.