Hi,
So in Messages (App Menu) > Preferences > Accounts you can see the iMessages account but the box (Enable this account) is unticked and under the account in the list on the left it says Inactive?
Which version of Messages have you updated to ?
What were you using before ?
NOTE: both Mavericks and Yosemite called their Versions "Messages 8" although they are different.
If the iMessages account is Inactive I am unaware of any way it can receive iMessages.
In the Main Window where the chats and conversations are listed what is the info in the left hand end of the text field to type new text before sending ?

It can say it is sending from AIM (and also the Buddy List name if you have more then one AIM account)

It can of course say iMessage.
If you go to the "To" spot it becomes a Drop down.
It will tell you if it is an Apple ID or an iPhone Number and whether it is iMessages, Text or another account that is being used.

This Conversation is currently addressed to the person's iPhone Number.
I list two Apple IDs for them as well (and a Land Line that thinks it might be an iMessages option).
If you can have AIM and iMessages chats and conversations with the same person the list will be longer.
This will tell you what sort of messages are arriving.
(Some may say Text as well)

8:40 pm Sunday; December 13, 2015
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad