I plugged my phone into my TV's USB port hoping to play video from my phone on the TV. This was not successful. It's been about 4 days since I disconnected from the TV and it still thinks it's connected.
I have turned the phone off and on, it may go away for a little while but keeps coming back. The top left status bar will have 2 arrows spinning in a cirle and when I drag downwards to see my notifications I see this:
MTP service status:
Connected to computer
My phone is an HTC Incredible 2 running Android 2.3.3.
I solved this by plugging in my phone to a computer and choosing Charge Only. It was using CPU and draining my battery until I fixed it.
As a worst case solution, you could try factory resetting your phone. You might also attempt to connect your phone to a PC and enable USB transfer, then eject your phone to see if this clears the issue.
When you say you turned your phone off and on, did you actually shut it down (hold down power button to get the menu), or just press the power button to turn the screen off? I would expect a shutdown and restart to clear this problem.