Close and reopen Outlook.
Open up Outlook, change the email account password to anything. try sending/receiving again. It will fail. Then enter the correct password when prompted. Let it do its stuff. Once completed change the password in the email account tools option again to the correct (original) one and try again. Does it work?
You must do all the steps not just say you have - don't cheat!
do you have "leave a copy of messages on server " set? If so how many days? Whatever its is reduce it down. Save it. Do a send and receive.
If nothing happens, repeat step 2 again.
Please note this is not "the" answer, but one we've found seems to work on quite a few occasions.
If you're still stuck you'll need some IT support! We recommend:
Oundle Peterborough area:
Andy Kemp 01832 720522
Wellingborough & East Northants:
Serendip-IT - Sally/Jim: 01933 229133
IT Tech Solutions: Mark 01604 808414
DV Support : Matt 01295 271545