Turn the pc on keep pressing F8, you will then see a menu and it should have safe mode there. If it doesnt then you will be in a boot menu (certain BIOSes have this) select your hard drive, press enter then start tapping F8 again and you will get to safe mode menu then.
As for which AV, i would suggest NOD32 available here for a free trial www.eset.com
. Or if you want a free one then try AVG or avast