email wiped out

just discovered that all but one email address is missing, nearly all
the folders are gone and i can not send or receive mail from my yahoo
web based email. i tried system restore.......no good, ran a complete
virus scan......no virus. am able to use my password to get into mail
but nothing works in there. i read about a yahoo mail virus but don't
know what it does so far. there seems to be no virus in here
tho........
appreciate any feedback on this........
.........running wn xp 2nd home ed.
thanks
jim