on my sister's win 2000 computer the registry cleaner remover the %1 command from the exe file extention causeing you to mot be able to open simple programs everything from the bult in calculator to CCleaner itself (if youre havint this problem then DO NOT restore from another computers registry thats what i did and i messed up the computer.
Actually that sounds like some damage from a malware infection.
You can reinstate the .exe association by using undo.reg from McAfee:
1. Copy the undo.reg data displayed at the end of this post into Notepad. Then save the document as including the quotes "undo.reg" onto the Windows desktop.
2. Double click undo.reg and then restart Windows.
undo.reg:
REGEDIT4; A Registry import file to undo registry changes made by Trojans; and Internet worms such as Prettypark and Backdoor-G.[HKEY_CLASSES_ROOT\exefile\shell\open\command]@="\"%1\" %*"[HKEY_LOCAL_MACHINE\Software\CLASSES\exefile\shell\open\command]@="\"%1\" %*"