my messages does not alert me when i get a video chat invite, no sound, no popup banner or alert.

my messages does not alert me when i get a video chat, only the green light goes on next to me camera. i have checked notification center and everything looks normal, if someone could tell me how to fix it or if another application is blocking it. this has been going on for a couple months, and it happened all of a sudden one day the alerts would not come up.

Thanks!