when ever i boot up my gateway windows 2000, sect pak 4, it starts to run, and then starts shutting on and off. eventually the screen turns a grey color, and then to blue. the blue window that comes up says"stop(c000021a) fatal system error. the windows logon process system process failed unexpextedly terminated with a status of 0x00000000 the system has been shut down". what do i do. it is my brothers comp and he bought it uses, with no backup disk, or whatever it is called. we know that it is infected, but had still been working. that is till a couple of days ago. now when you turn it on, that is what happens. it keeps repeating the same process, shutting on and off, but never getting booted up and online. help me please?