Computer stuck in Logg in Logg off loop

It all started when I noticed that I had a Messege stating that my Windows automatic updater was turned off, I opened up the security center and it said it was on.  I went ahead and clicked the button to make sure and nothing would change.

Also when explorer was open I would get other windows opening with various ads and sometimes a fake window security saying I had multiple viruses, so I would do a scan with McAfee and nothing would show up.

Later one night I was not on my computer but had not logged off it was just up with screen saver and all of a sudden there was loud advertisement noise coming from it, I shut everything down and shut it off for the night, the next day I had trouble logging on (can only log on if conected to the internet otherwise no icons or start menu come up)  I tried to run McAfee again and this time it listed over 1400 viruses and not all could be quarentined.   I tried to do a system restore but after I picked the date and clicked next it would not respond and eventually froze.  I did another shut down restart and now it logs on then goes to a shut down and loops.  I have not tried starting in safe mode yet but if able what are the first steps I need to take.

I have no file shareing software downloaded

I may have an old cracked software on my system (can I remove it in safe mode?)

I do not have Hyjack this installed or anything other that McAfee security suite.