I have Intel Pentium 4 computer with Intel processor 3.2 GHz with 512 DDR RAM. I am using Windows XP SP2 operating system. Recently I change the PRODUCT key of Windows OS from pirated to genuine one. But the problem after updating the product key is the antivirus AVG – free edition is giving message that “AVG is not able to recognize your license No.” It tells to either activate or reinstall. While doing so it is asking for license no. which I don’t have. So please help to solve this problem.You are going to need to work that out with AVG.

http://forum.grisoft.cz/freeforum/Quick check, were you using the free version of AVG or did you buy a copy from them? If you were using the free version just uninstall, and install the new version. If you bought a copy the follow Evilfantasy's advice.Quote

Recently I change the product key of Windows OS from pirated to genuine one.

• GO in to Revo, right click what you want to uninstall and choose Uninstall.
• Next choose Advanced Mode
  
• This will launch the programs built in uninstaller and go through the normal uninstall process.
• Once complete: In Revo Uninstaller click Next and Revo will scan the registry for leftovers.
  • This scan can take several seconds.
• Once the results are shown look at each one to ensure they are all related to the program that was uninstalled.
• Choose Select Allthen click Delete
  
• Click Next and Revo will scan for any files or folders that were not removed.
  
• If any files/folders are found choose Select all > Delete