didn’t change anything ? Did you update your application on the Panda?
I’d just suggest you erase the device and reapply the netmf firmware, as @ John suggested. That should then let you get back to a working state. If you did make code changes, it’s possible you just have coded something that causes the device not to respond fast enough - at least if it works with no application installed, then stops working after you deploy your app, it becomes clearer that there’s a code issue to dig into