On a Pentium system upgraded from 5.2 to 5.9, none of the TeX engines work. For example "tex foo.tex" complains that the file tex.fmt is missing. If you run "texconfig", is does a lot of initial work before providing the usual initial dialog box. If you immediately quit at this point, TeX (and friends) will now work fine.
Oops. This looks like a re-report of bug 2080. Sorry!
*** This bug has been marked as a duplicate of 2080 ***