List of Files Not Available in Apps

I am using WindowsXP,SP2, and until a few days ago in programs I use, there was a list of the most recent files opened under “Files” in the menu bar. In Excel, the task pane listed my most frequently used files. I looked the problem up in the MS knowledge base, and it said I can no longer list the files because I make a change in IE6 using TweakUI. I didn’t use TweakUI, I did nothing. I have been having small problems like this in the past few months. When I load the Windows CD, it loads some files, then tells me that the CD is not recognized as WinXP CD, so I can’t use the repair function. I am unsure what to do now. I never realized how much I rely on those lists.