Help us: "Machine state: Closed"

Hello,
So heres the problem:
Our 3D- Printer (Prusa i3 with 1.3a Sanguinololu, Atmega 1284P) was just working fine. But suddenly we couldnt connect to Printer anymore. Cura just said: "Machine State: Closed". It isnt a problem of Cura, because we couldnt connect with Pronterface either. We are able to connect with Arduino, but when trying to upload the software, Arduino starts to do so, but after that nothing happens.
We think that its probably some probleme with the Sanguinololu board but we have no idea what it could be.
Before buying a new one I wanted to ask, if anyone has an idea what could cause the problem. If you need more information just say it.

I hope somebody is able to help us.

Make sure power is off pull everything off of board and try to connect. Are you using a standard usb cable (5v power from the computer to the sang 1.3)? It is a known issue with the board and can cause problems.