^ not a good idea, any so-called fix-all tools have a way too high of a chance to make your system totally unusable.
First check for viruses/spyware, there is a guide in the main XP forum page. If that did not help, you should try to do a System Restore to before your issue happened http://support.microsoft.com/kb/306084.
If that does not help, do a Repair Installation of Windows. http://michaelstevenstech.com/XPrepairinstall.htm
<-- good guide, just read the whole thing before starting.