Windows Security Center service can't be started

Solution 1:

Might sound silly, but you didn't mention if it's persistent... does it continue after restarting the machine?

Have a read through this Microsoft KB, I'll include the jist of it here.

1. Click Start, and then type services.msc in the Search box
2. Under Programs, click Services.
3. On the right side of the window, locate the Security Center service in the list of services.
4. Right-click Security Center, and then select Properties.
5. From the Startup type drop-down list, select Automatic (delayed start).
6. Under Service Status, click Start.
7. Click Apply, click OK, and then close the Services window.

If you get any error messages, post them up here as they will be key to what the problem is (there is one example of an error message and the fix for it on the linked KB.)