Another friend's computer. This time if it is shut down normally it restarts normally. However if the 13A plug supplying the mains is removed after shutting down normally, then replaced, then when it restarts it comes it freezes with a dark blue screen - not the BSOD. It then has to be shutdown by holding the start button for four seconds after which it starts with the screen advising of an abnormal shutdown. If normal start is then selected it starts normally. This friend likes to pull out all plugs at night so this is a bit of a nuisance. Any suggestions as to why this is happening.