Hi there,
Have you checked if your profile was changed with another one ?
try checking in "controlpanel" - "e-mail" (e-mail in win7 don't know in win8)
if you have more than one profile just check the other one as a "standard" profile !
if you have corporate mail it should be an OST-file, (offline folder cannot be opened as a PST-file)
You can search for PST-files, can be opened in outlook as a file (NO DOUBLE CLICK). The PST file should contain your old mails !
Let us know if it solved something !
Cheers, Louise.