What is the best and free anti-virus software or website to use?

Hi, i had my laptop about 3 weeks ago and 1 week ago i went to log into my account and after i put my password in and clicked enter it said welcome with the loading icon and just stayed like that. It did this every time i tried to log on. I could start it in safe mode. I just wiped my computer clean and started again with the disk. The same thing happened yesterday. I do not have a virus after doing scans from Mcafee and two other virus scans and they all found nothing. I have restarted my whole computer again and i am desperate to know what happened and how i can stop it from happening Again. My OS is Windows 7. Thanks  forex robot

嗯， 問問那個威武雄壯滴！估計套木馬的能力也很強， 哈哈。。。