I have Me on my old PC and you only have to sneeze and it locks up...I also have the same AV software on it and my new one (XP) and can't recommend it highly enough. When downloading the AV software/updates, it is extremely important, moreso with Me, to exit any PopUp/Advert Stopper programs you have running. It is also very important to let the d/l complete before touching anything. The first thing is to get your PC running again so try to boot up normally. If it won't, boot it in safe mode and run in-depth scan disc (takes a while but you have to start somewhere). When its normal, log on to the AV site\My Account\ then try to download it again following all instructions to the letter. The download should detect/correct previous files and install correctly. Good luck.
PS Me (mine anyway) locks randomly and its easy to wrongly associate the problem with something else..