Mac recognising external soundcard but rejecting it as input output

Hi - overnight my macbook has stopped working properly with external soundcards (I have tried this with two different soundcards). My computer recognises the soundcard is connected and it shows up in sound preference options. However if I select the external soundcard as the input / output source either from system preferences or via programmes like Ableton, then it activily rejects it and freezes/crashes programmes.

I have tried uninstalling thoroughly all the drivers for soundcards (namely Apogee Duet) and reinstalling but the problem continues. I've had no problems with my Macbook ever, even though it's around 7 years old. I'm running 10.10 Yosemite and it was all working fine with the system before. Haven't been able to find any answers online, no one seems to have had this exact problem as the computer is recognising the external soundcard and my usb connections are working wth other midi type stuff.

Any ideas?