Mail problems trigger crisis!

Hi:

A few months back I deleted a plist file and archived and reinstalled my system folder to deal with what was apparently corruption in my Mail app file. Unfortunately several apps stopped working after the archive and re-install (mail worked again for a time). Now Mail won't receive mail--so I'm back to having problems with it-- and I am also having problems with accessing .mac webmail, so basically I have slid into complete paralysis, unable to access email and with some apps not working on my desktop! Any help would be a lifesaver as I am on deadline with projects and stymied.

Thanks!

Cory