installing MSE could be a huge mistake.
my experience with >> on a LEGIT copy of xp pro i installed after i got a nasty malware from a flash add i had my firewall down for 10 mins and this happened, anyway i installed MSE thinking it would take care of t, installed rebooted,
windows just got stuck on log on screen , windows just refused to boot, so booted in safe mode, luckily i had malwarebytes installed updated and cleaned that malware , cleaned the registry entries it had made etc , it was totally gone, booted out of safe mode , windows still refused to boot, well i though maybe that something still remained from that stupid virus soi boooted off from Hiren's BootCD , run the virus scanner from there, all was clean, ran some disk tests everything all ok , by now i was getting bugged as that was the only p.c i had access to on that day , so booted into safe mode again , went into system logs to check what is happening and guess what MSE error : your windows license has expired login denied !!!!
and this happened on a legit copy of xp pro i had , anyway windows is so hackable all i had to do was to change the license to a PIRATED, one remove MSE make some changes to registry , and i was good . guess MS likes pirated copies better then legit ones. anyway i would never recommend this to anyone . there is very good chance that you get locked out your system even on legit copies , the risk is too much i knew how to get of that but 70% ppl could get stuck and would be forced to do a reinstall.
stick to nod32 and a good software firewall, infact a good hardware firewall combined with a good software firewall like outpost pro and you really don;t need av.
So that was the OS problem. you should have contacted
microsoft about the problem if you had a legal copy of OS.you had a problem maybe coz your serial key was used by too many people so microsoft must have black listed it.
about the virus problem no antivirus is 100% efficient with viruse. also check the resources used when MSE scan is under progress as compared to other. MSE is always lighter.
also again different users is comfortable with different antivirus
some AV are much lighter some are efficient with threats. MSE is balance in beetween considering its free and full version i consider it good AV!!!!