Hi. Random reboots are usually caused by heat, memory, driver issues or the power supply. You need to investigate each possible cause to rule it out or fix it. Check your fans, make sure they are all working and that your computer is free from dust, cat hair etc. You can go to http://www.memtest86.com/
and get memtest86, test the memory. You can check the system event log to see if it gives a clue as to the cause. Go to my computer, right click manage, and view the event log for the time of the last reboot. Right click properties for details. You can also send a report to M$ and view their knowledge base for possible solutions.