disk cleanup and defragmenter dont work

Xref: kermit microsoft.public.windowsxp.perform_maintain:180190

hi,
alright, im sort of computer illiterate, so these
questions might sound pretty dumb, but anyway....
when i try to use disk cleanup and disk defgragmenter,
nothing happens at all, they both worked a few weeks ago,
and i havent touched them since. also, my whole system
has been running extremely slow for the past few days.
ive virus scanned, deleted cookies, deleted dozens of
large files, ect, and nothing will make it run faster.
does this have anything to do with the disk cleanup and
defrager not working? any idea how to fix this? do i need
to upgrade or something?