Question Author
OG - many thanks for interest and reply (good name, by the way, - describes me really!). Also for link.
There are 6 ports at the back of my pc, colour and mark:
top - Grey side spk, Black rear spk, Orange ctr bass. under - Pink mic in, Green front, Blue line in. They all have symbols. I assumed at first that it must be the black port, no good - all the other tried as well. Everything is switched on ok so I'm stumped. I must see if I can test the speakers somehow.