Gmail is "inactive" in Apple Mail?

[Imola Ghost]

For some reason I'm not getting my Gmail, so I went into Apple Mail's preferences and under Accounts, gmail says it's "inactive".

I haven't changed or did anything, so what is going on and how to fix this? This just happened on my 27" iMac and now it's happening on my 13" MBP.

 

[JediMeister]

Posting on my iPod touch, so not 100% sure about this, but in Accounts there should be an Advanced tab along with Account Information and Mailbox Behaviors. Is there a checkmark for making the account active?

In front of my Mac now, under the Advanced tab will be "Enable this account"; is this checked? By the way, your Gmail account, are you using POP or IMAP access?