Have you tried a System Restore to a time before this happened?
Otherwise try this:
"Method 3: Reinstall the Search Companion Files
To resolve this problem without obtaining the hotfix or installing Windows XP SP1, follow these steps:
Log on to the computer by using an account with administrator permissions.
Click Start, click Run, type %systemroot%\inf, and then click OK.
Locate the Srchasst.inf file.
Right-click the Srchasst.inf file, and then click Install. This reinstalls the files that Search Companion uses.
NOTE: You may need your Windows XP CD-ROM to finish installing Search Companion. This issue may occur again if you have Search Companion open when you connect to your ISP.
The problem may continue to occur after you disconnect from the Internet because the files that have been corrupted are cached. You can view the appropriate files (open them with Notepad, not Microsoft Internet Explorer) to determine the source of the corruption. The files that are involved are:
Balloon.xsl
Bar.xsl
Lclsrch.xml
WORKAROUND
To prevent this problem from occurring, make sure the Search Companion is closed before you connect to your ISP."
.....or go directy
HERE !
Hope it helps.