Windows version?

IE version?

Run a /thorough/ check for hijackware, including posting your hijackthis log
to an appropriate forum.

Checking for/Help with Hijackware
http://aumha.org/a/parasite.htm
  http://aumha.org/a/quickfix.htm
  http://aumha.net/viewtopic.php?t=5878
http://wiki.castlecops.com/Malware_Removal_and_Prevention:_Introduction
http://mvps.org/winhelp2002/unwanted.htm
http://inetexplorer.mvps.org/data/prevention.htm
  http://inetexplorer.mvps.org/tshoot.html
http://www.mvps.org/sramesh2k/Malware_Defence.htm
http://defendingyourmachine2.blogspot.com/
http://www.elephantboycomputers.com/page2.html#Removing_Malware

When all else fails, HijackThis v1.99.1
(http://aumha.org/downloads/hijackthis.zip) is the preferred tool to use.
It will help you to both identify and remove any hijackware/spyware with
assistance from an expert.  **Post your log to
http://forums.spybot.info/forumdisplay.php?f=22,
http://castlecops.com/forum67.html,
http://forums.subratam.org/index.php?showforum=7,
http://aumha.net/viewforum.php?f=30, or other appropriate forums for expert
analysis, not here.**

If the procedures look too complex - and there is no shame in admitting this
isn't your cup of tea - take the machine to a local, reputable and
independent (i.e., not BigBoxStoreUSA) computer repair shop.

In addition to PA's suggestions, it is possible the registry was blocked by
AV or Firewall software.

Backup the registry before doing the following:

Run>Type in Regedit
Go to Hkey_Current_User\Software\Microsoft\Internet Explorer\Main
In the right pane, right click on Start Page and select Modify
Type your Home Page url and click Ok
Close Registry
Reboot System for changes to take effect

It would be a bogus/spyware security center.

Down load "Spybot Search and Destroy", get the updates for it, and scan your
system.

If it can not remove everything, reboot, hit F8, go into Safe Mode, run
Spybot again to delete anyting it could not remove in dynamic mode.