Internet Explorer at 100% utilization on power up.

On power up off desktop pc running extremely slow. Using Process Explorer I
can see two sessions of internet explorer are open, one of which is using all
the procesing power. If I kill both of these the pc works ok, although
occassionally they reopen. In which case I can kill them and continue to work
ok. How can I stop these from starting up? I am currently on IE7 although
this still happens if I remove IE7 and run on IE6. I am also using Winows XP
home.