You must have an Antivirus on your system if you wish to connect to the internet, or you will very quickly have an infected computer. I am afraid that is what has happened to your system.
Probably the safest thing for you to do would be to reformat and reinstall your XP operating system, to wipe it all clean and start afresh.
We can try to do some temporary repair of your computer, nevertheless...
Please download Malwarebytes AntiMalware from www.malwarebytes.com , update it, and run a scan of your system. Please fix any problems it finds.
There are several good antivirus software available today, some for free. If you do not have AV installed, please download Avira free by clicking here
, but do not install it yet. Just save it on your desktop.
If you had a previous version of AVG that is no longer up to date, please go to AVG's website
by clicking here
and download and install the AVG remover for your system (probably AVG32 for xp). This will remove any remnants of your AVG installation from your computer.
Disconnect from internet, and turn off any anti-spyware programs you have running.
Go to control panel> add/remove programs and remove any anitivirus programs installed on your computer. You must use ONLY ONE anti-virus at a time. If you are sure there are no other programs installed, run the setup Avira that you saved to the desktop. Once the Avira AV is installed, reconnect to the internet and update the program. Then run a complete scan of your computer. Fix any problems it finds.
Go to windows update and download and install all critical and security updates available for your computer.
Go to Microsoft by clicking here
and download and install Windows Defender if you do not already have it on your system. Run a full scan.
Report back on your results.
Please read this article about when to flatten and reinstall
I hope this will help you to resolve this issue. If you have further questions please respond with a comment to this thread.
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