Just downloaded Kings quest 8 but but when starting game , <copying files to hard drive > appears then at about 25% complete it locks up/ any ideas or is there Tech support for GoG somewhere?

Did you try running it as administrator and/or disabling antivirus?

Just to clarify: Are you talking about installing the game, or actually running it after installation is finished?

And, yes, GOG has their own tech support department -- there's a link to the 'Support' section right next to your 'Account' menu.
Here's the link to the specific support page for King's Quest 7 + 8: https://www.gog.com/support/kings_quest_7_8
And if nothing there (or here) solves your problem, click "I can't find solution for my problem" in the "Contact our support team" box on the right side to send a support request. (Just be aware that they're down to a skeleton crew on weekends, so if you wind up contacting them this weekend, know that they likely won't get back to you until at least Monday; also, be advised that they're located in Poland, so their normal business day begins and ends several hours before ours. ;) )

Take a look at this thread :

 ▪  <span class="bold">King's Quest 8 - Unplayable</span>   (solved)