Go to www.grystmill.com and read the "Clean Boot" article. Set up a proper
Clean Boot, then use MSCONFIG (explained in the article) to determine if any
of the items in the Startup list are causing the auto-launch of IE. The
easiest way to do this is "by halves". If IE doesn't restart under a clean
boot, then re-enable half of the Startup list. Restart and see if the
behavior returns. If so, then try only enabling the other half -- to make
sure there's not more than one item involved.

Assuming only one half contains the problem item, then re-enable all but
half of that group (the previously enabled half of the total.) Again, if the
behavior returns, then you know that it's in the group you just re-enabled
(one quarter of the total group.) Proceed to again re-enable all but half of
the group that you now know contains the culprit, continuing until you have
narrowed it down to just one item that when enabled causes the problem.
Again, it might be more than one, but the halves method is much quicker for
narrowing the field.

Post back with the name of that item or items, then read the Security
article at that same site. Unless you recently installed some program that
is set to do this kind of thing, you almost certainly have a malware
infection.