Tip for you vivek: I assume you are from India looking at your name...so...here is what I see people do mistakes everyday in india...so some things for you:
1- Never turn off your AV ever even if you are in a computer shop or cyber cafe and never do it on anyone's saying.
2- Remember no AV detected 100% because everyday 50,000 viruses come out.Use avast [one of my top pic AV] I recommend it to all of my clients and they are clean and protected from this crap.
3- Always exercise self caution when using USB's and browsing internet,never watch porn or click on links that you dont know what they are about on facebook,twitter etc.
4- Disable autorun feature in your PC which viruses use to launch automatically from USB;s,see here on how to do it:
http://support.microsoft.com/kb/9677155- Stay away from dubious Antivirus products like NPAV,QuickHeal,K7 etc and only use 1 AV program on your PC,you pair 1 AV program with Malwarebytes Antimalware which runs alongside with any AV and helps protecting your PC,see: malwarebytes.org
6- DONT use cracks,illegal,hacking software and stuff as they come bundled with viruses.Keep your windows and softwares up to date.
7- Essexboy will link you to a guide after he confirms your problem is solved,read and follow the guide carefully.
8- Read my tips again.