Connecting ipad to other computers, for importing selected music I have a 1st generation ipad. I want to put selected music on it - not sync my entire collection.

I've managed it before, a year ago but forgotten exactly how and this time I can't get the ipad to appear in iTunes. I've tried to connect from both a Windows XP desktop, from a MacBook running OS X Yosemite 10.10.4, and from an old PowerPC, all 3 of which have the desired music.

How do I trouble shoot this?
Is using iTunes the correct way to go? I seem to remember just doing some kind of basic file copy, previously.
This, apparently, was caused by a faulty USB cable.