Thank you all for your responses.
I now have a Sennheiser HD 25-1 with a jack. When the shop built my PC, (a Carillon AC1), they left a test project of three tracks; Plugins Padshop, Hypnotic Dance and Symphonic Orchestra. I click the transport and the ‘curser’ moves along the tracks from left to right,. I can see the led’s move in the Mixer, but there is still no volume in the 'phones. On the back panel of the PC there is a multi-pin plug (plugged in) with 8 sockets coming out: Two Din L&R, two Jack sockets Mon L&R (Monitor), two Jack sockets L&R Main Out, and two Jack sockets for Main In, L&R.
This multi-pin plug is plugged in to the M-Delta Audio card.
I think that is all anyone needs to know. But my question is… Is there something somewhere on the mixer, or anywhere else, I need to ‘turn on’ to get the headphones to function. The only positive thing I noticed with all of this was when I was changing the plugs on the multi-pin plug to the headphones. There was a crackle when I plugged the phones into the Monitor ones.
If anyone has experienced anything like this, I would appreciate their advice.