Terri, are you running Security Essentials on your new Windows 8 computer? If so, did you disable the Windows Defender first? If you tried to install Security Essentials, hopefully it prompted you that you can't run it unless you disable Defender first. You can't run both of them at the same time.
When you open it up, does it say it's been turned off?
In my PC corner for the winter, gaming, knitting and reading.