Can't Access Calculator / Paint / Word Pad

How to figure out why the Windows Accessories Programs "Calculator," "Paint," and "Wordpad" appear to have been disabled in my PC (XP Professional)? I tried to find where the "Calculator" program may be lodged in the hard drive, for example, so as to bring back the application from wherever it is apparently hiding. I typed "C:WINDOWS/system32/calc.exe" into the "Run" command. The message box that opened read like this: "Windows cannot find C:WINDOWS/system32/calc.exe." The message box then suggests to "....click the Start button, and then click Search." "Search" could not find the file. But it was accessible before from the Start-> Menu->All Programs->Accessories.