Digitech GNX3000 help please!?

So . . . i have a Digitech GNX3000 Guitar Workstation. it worked fine up until now. When i turn it on, my amp emits a great screeching noise and the USB Active light flashes red. In addition to this, my guitar wont register with it. When i strum a note nothing happens. however, when i play a drum beat on it, it works fine through my amp. any suggestions are greatly appreciated thank you. :)