NEVER use McAfee or Norton. They are like parasites to your system. To stay safe I have always used anti-viruses like Avast or AVG (both free) and never had major problems. I combine them with SUPERAntiSpyware (also free) to deal with suspicious crawlers and cookies, etc. I had a hard time with McAffee on my mother's new laptop because it caused trouble on the network too and installed the correct drivers and chipset (make sure your computer always has the latest up to date drivers) THEN installed AVG + SUPERAntiSpyware.
Those things are lightweight programs that won't suck the life out of your online experience.
Good luck, I hope this helps, I'm only half-witted when it comes to informatics.
#1: Uninstall McAfee
#4: check your firewall settings, make sure Windows Live Messenger/Skype/etc are unblocked.
EDIT again: http://www.ccleaner.com/ This could help you get rid of the registry files leftover from the McAfee installation, since as a self-respecting parasite program it will make it difficult for you to get rid of it and force you to buy it again for some obscure unexplained reasons. CCleaner deals with that kind of crap, also with mallware crawlers and glitches that confuse your anti-viruses and turn your life into a real-world hell.