Here is the process:
1. Click on Sheet1, cell x.
2. Press "Ctrl + K" or "Insert > Hyperlink" to open the "Hyperlink" dialog.
3. In the "Jump Target" field, specify Sheet4!A5.
Thanks,
Having yet another senior moment....
I tried that earlier, a few times and got some strange results, none of which were correct. Wanting to open new files etc.
After a reboot, I now have it working as per your suggestion.
Cheers, panic over
Again thanks.