ok...
go to start menu, select Run, type
regedit
this gives you access to the windows registry - the thing that makes windows slow...
navigate to HKLocal Machine\Software\Microsoft\Windows\CurrentVersion\Run\
there you should find the virus launcher - Microsoft Diagnostic - delete it
there will be other normal keys for programs that you expect to run when windows start - like anti virus, messenger, etc - this is what this section of the registry does
be careful though as editing the registry can fuck your machine

have fun