A screen Pops up from nowhere and says You are infected to a virus, and when you click on it it will forward you to a website offering their Anti-Virus. Right?
This is a Stupid adware, Last time i got infected to this one and I couldn't do anything about it, Norton Antivirus, Internet Security, non worked. So I installed a fresh windows.
I suggest you to install Microsoft Antispy I hope that it works. If not, try searching in your programs and uninstall any unknown or suspicious program (be carefull, some programs have wierd names but they are not adwares, they might be some necessary system programs). These adwares are mostly hidden and you cant simply uninstall them from control panel, if you couldn't find it in Add/Remove Softwares in control panel you should check your C Drive Program Files folder, you will probably find a folder for the adware, if it exists its not hard to find.
If it is neither in your Control Panel nor in your Program Files, then it might be hidden somewhere in your Windows folder, and if you delete anything from your Windows folder, most probably your windows would not operate properly. In this case, the only remaining choice is installing a fresh copy of windows. Make sure to use Windows XP Service Pack 2 , download Microsoft Antispy, and keep your windows up to date. Don't open junk websites, do not let your web browser install anything unnecessary unless you know the publisher, I also suggest that you use FireFox as your web browser, it is much more secure comparing to Windows Internet Explorer.