microsoft isnt THAT retarded but its pretty dumb, anyways you should have an antivirus and a reformat is pretty apropriate after having a computer for like a year or two

If you do want to reformat put in your windows xp cd boot from that, then follow the instructions! Delete partition > Install windows ( dont do the quick install) and have your windows key ready, its like a blue green sticker on your computer, or somewhere taped onto a cd cause if you dont have it dont reformat if not activated in 30 days itll iunno but its bad!