Q: No sound coming out of Scarlett 2i4

I recently bought a Focusrite Scarlett 2i4. I use it along with Logic Pro 9. It was working fine up until I plugged in my guitar into one of the inputs and then unplugged it. Since unplugging, I have not been able to use the monitor or headphone function as there is no sound coming out. I Have tried replugging all cables but this has not worked. There is no focusrite tech support till the 2nd of January. Any suggestions as to why this is happening and how I can fix it will be much appreciated.

Thanks