mail not working

MacBook Pro 10.6.8 / macmail & gmail / IMAP / Airport

Mail icon still on dock as it has always been. The little light is under the icon stating mail is working.

When I click on the icon nothing happens.

Click mail icon / (menu) quit, nothing happens.

Click mail icon, and the desk top toolbar is correct for mail, but when clicking mail in toolbar, 'quit' is grayed out.

Mailboxes says All accounts are on line. I have clicked synchronize accounts.

Mail Activity has all red lights.

Connection Doctor has all green lights saying I am connected to server.

Airport preferences say Airport is on but Ethernet is not connected. Ii says either the cable for Ethernet is not plugged in or the divice at the other end is not responding. I checked the Ethernet cable on motom and Airport but cannot restart computer because 'mail' will not close, stopping restart.

My older Imac desktop is getting mail as usual.

Thank you to anyone for help.