Hi Robert,
This issue could be due to some incorrect settings or due to some other service restarting the computer. To be able to help better, please answer these questions:
1) Did this issue start recently? Do you remember making any changes prior to this issue?
2) What happens after it restarts? Does it go to sleep mode?
Let’s try these troubleshooting steps and check if it resolves the issue:
Method 1: Power Troubleshooter
The Power troubleshooter can detect and fix any errors or incorrect power settings. Refer to these steps to run this troubleshooter:
a) Click on the Start button and then the Control panel.
b) Change the view by option on the top right to Large icons.
c) Click on troubleshooting and click on the view all option on the left panel.
d) Run the Power troubleshooter.
Method 2: Create a new power plan and check
If the troubleshooter didn’t detect any issues, then I would suggest you to create a new power plan and check. Refer to this article for more information:
http://windows.microsoft.com/en-us/windows7/change-create-or-delete-a-power-plan-scheme
Method 3:
If the above steps didn’t help, then I would suggest you to boot the computer in safe mode and check if the issue persists.
Step 1: Safe mode
I would suggest you to boot the computer in safe mode and check if the issue persists. Refer this link to boot the computer in safe mode:
Step 2: Clean boot
If you don’t face this issue in safe mode, then we will have to perform a clean boot procedure to find out which service is causing this issue. Refer this link to perform a clean boot:
http://support.microsoft.com/kb/929135
Note: After troubleshooting, reset the computer to start as usual. Refer step “How to set the computer to start as usual after clean boot troubleshooting” under more information.
If the issue still persists, I would also suggest you to post the event viewer logs here, so that we can check and identify the exact issue. Refer these steps:
a) Go to the Start Screen, type in Event Viewer. This will bring up the Event Viewer tile, Click to open the event viewer.
b) In the left pane, expand out Windows Logs. Click on Application log and highlight the first event in the log and use your arrow keys to scroll down.
c) Most of your event will be Information. You may see Yellow Warnings or Red Errors. If you see any red error, you can double click on it to bring it up and copy the contents to a document.
Hope this helps. If the issue persists, please get back to us with the Event viewer logs for further assistance.