Error message 'Product ID is invalid'

Hi,
Everything was working fine till yesterday but after getting a virus warning from my norton while browsing internet, i did a full system scan and after i rebooted the windows activation status got disabled. and when i boots it gives me message the Product ID is invalid .
What to do now?

Your Software Licencing Service may have been disabled. To check the status:

• Click Start and type Services or services.msc in the search box and then click on Services under Programs section of the search results on top pane.
  
  
• If User Account Control ask your permission to continue, click Continue.
  
  
• Scroll down the list to the service Software Licensing and double-click it.
  
  
• In the properties window of the Software Licensing service, set Startup type to Automatic.
  
  
• Click Start to start the service. If the status is already running, click the Stop button and confirm with Yes to stop the service. Restart the service by clicking the Start button.
  
  
• Click OK to exit from Software Licensing’s Properties window and close the Services window.
  
  
• Go to www.microsoft.com/genuine and click the Validate Windows button to re-validate Windows. If you have problem with system updates, re-initiate system update.

1. You have an issue with your original Product ID, then call Microsoft and explain your dilemma. No doubt, they will be able to assist you.
   
   
2. If 1 is not the situation, then read the following link: -
   
   http://www.microsoft.com/piracy/activation.mspx

Refer this guide http://support.microsoft.com/kb/906893 . Hope this will help.

This three little letters will prevent you from entering the Microsoft support
areas:

• If you purchased your computer with OEM version installed, Microsoft will provide absolutely no support. You must go to the vendor which supplied the OEM version.
  
  
• If you purchased the OEM version and installed it yourself, Microsoft will probably tell you that you are not a recognized OEM vendor (you don't build computers for a living) and again will not support you.
  
  
• On the off chance you do build computers for a living, you would have already known this and known how to contact Microsoft regarding your issue that they most likely still won't support other than Knowledge Base, Newsgroups and Forums.