1. Have you done any recent changes on the computer?
You may check for the service and the "Dependencies" for the service.
You can try starting and stopping the security center service and check. Also check for the dependencies status-
a. Open Administrative Tools by clicking the Start button, and then clicking Control Panel. In the search box, type administrative tools, and then click Administrative Tools.
b. Double-click Services. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
c. Right-click the Security Center Service and then click Properties.
d. On the General tab, next to Startup type, make sure that Automatic is selected.
e. Also under Service status, click Stop, and then click OK. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
f. Then click Start on the same service.
f. Now under properties click theDependenciestab.
Look for the “Dependencies” under “Remote Call Procedure” and make sure all the dependency services are running and set to “Manual” or “Automatic”. Check if all services are started.
I would suggest you to perform a SFC scan and check.ToPerform a SFC Scan -
a.Click Start, click
All Programs, click Accessories, right-click
Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow
b.Type the following command, and then press ENTER:
A message will appear stating that 'The system scan will begin'. Be patient because the scan may take some time
c.If any files require a replace SFC will replace them. You may be asked to insert your Win7 DVD for this process to continue
d.If everything is okay you should, after the scan, see the following message "Windows resource protection did not find any integrity violations"
e.After the scan has completed, close the command prompt window, restart the computer and check.