I wish to install Elements 11 following a disk crash and Windows O/S
rebuild on a new disk. However, I did not and now unable to deactivate
the install on the crashed disk. Is there a way round this?
Yes, it's a common situation. First, you are allowed two activations, so if the second one has not been used, it's still available and you only have to reinstall and 'sign in' or 'activate' with your license key (available on your Adobe account).
Otherwise, use the contact option in the Help (Customer Care) for a chat or phone session. They will deactivate the old computer.