1) SMPS Damaged: Faults in SMPS is one of the most reasons of restarting a computer. So If you facing computer restart issue then quickly check the status of your SMPS. Check whether fan of SMPS is working or not. If Fan of SMPS doesn’t works then power supply gets heated and tour computer restarts itself. Keep clean the SMPS if there is dust.
2) Check computer FAN: There is another fan beside computer beside motherboard, check if it si working properly, If there is a fault in it then in this case as well computer restarts automatically.
3) Memory (RAM/Hard Disc) Damage issue: Check the RAM and hard disc of your computer if working fine, If there is problem then replace it with a perfect.
4) Problem in installation of window: If there is problem in window then in this case as well it can cause to restart a computer. Check window whether it is properly installed.
If there is any problem in window installation then you can fix this issue by just making some changes in setting.
Click on My computer icon available at desktop or click on at available in Start menu. Then click on properties, now click on advanced system settings, Now click on setting option available under Start Up and recovery, Now uncheck the option of Automatically restart and click on OK and save it. Note that if there is a problem in SMPS, Computer FAN or RAM OR Harddisc then this will not work, This method will work if there is any issue in your window and it restarts due to failure issue generated by window.
5) Problem in installation of driver: Check whether driver of your computer is properly installed.