Why Windows Security Center Service is not turning on

Sometime window security is not turning on because of various problem. To turn on the security centre service follow the following steps.
To access the console type Services in the Start Search field, and press ENTER. You will need to click Continue if prompted to open the Services window.

In this window you need to locate the Security Center service right-click it, now select Automatic and select Start. When the service fails to start you will receive an on-screen error message.

Post the error information here so that we can better understand why the service is failing to start.

Note you need to disable any security software on your computer and check for the issue.

Now try to start your computer with default administrator account and check for the issue to do that follow the below provided steps.

1. Open the Local Users and Groups manager.
2. In the left pane, click on the Users folder.
3. In the middle pane, right click on Administrator and click on Properties.
4. To Enable the Buit-in Administrator Account -
     a) Uncheck the Account is disabled box.
     b) Go to step 6.

5. To Disable the Buit-in Administrator Account -
   a) Check the Account is disabled box.
6. Click on OK.
7. Close the Local Users and Groups window.
8. Log off, and you will now see the built-in Administrator account log on icon added (enabled) or removed (disabled) from the log on screen.

NOTE: Click on the Administrator icon to log on to the built-in Administrator account.

Now from the above provided steps you need to check whether you are able to resolve the issue, if you are able to fix the issue with default administrator account then you need to follow the below provided step to create a new user account and check for the issue.
http://windows.microsoft.com/en-US/windows7/Fix-a-corrupted-user-profile