i pefer AVG 8.5 , uses less memory and quick protection, which you can download full version from rapidshare , macafee ya ! that is also good anti-virus software , i used to use that before but now i love AVG 8.5 . 

To boot your OS in safe mode,  At the time your PC is booting ( After you turn on your pc ), Keep hitting DEL and then you will see a  Boot manager window and  press F8 and choose option safe mode thats it !