|In Windows XP there's a feature called Windows System Restore, this will restore your OS to a state previously saved by either you or Microsoft Windows.|
Follow these instructions to restore:
1. Start Menu > Run
2. Type or paste in.. %SystemRoot%\System32\restore\rstrui.exe ..then press enter
3. You should be on the System Restore program, proceed to the option labled "Restore my computer to an earlier time"
4. Chose the appropriate restore point and continue
Once you've finished, it's VERY important you run a virus scan on every HDD, and make sure you use updated Anti-Virus software. AVG with the latest upgrades would suffice. If you perform the scan from Safe Mode, you'll have a higher chance of catching and removing a possible infection.
In future, whenever you have downloaded something, I reccomend you scan whatever it is. Also, make sure your Anti-Virus software is updated.
Best of luck.
...It is simply phsychological analysis consisting mostly of theories I myself have to decypher and deter their respective plausibility...