Unable to sign in

if you have a non-current os, your default browser must support tls 1.2, https://helpx.adobe.com/x-productkb/multi/eol-tls-support.html

to test your default browser's tls you can use , https://clienttest.ssllabs.com:8443/ssltest/viewMyClient.html

otherwise, confirm that you can connect to the secure adobe servers by reading, http://helpx.adobe.com/x-productkb/policy-pricing/activation-network-issues.html

do you see both logos after clicking "link"?

if you can and still see a connection error try these steps, https://helpx.adobe.com/download-install/kb/common-network-connectivity-issues.html

if those all fail, white list the adobe network endpoints, https://helpx.adobe.com/enterprise/kb/network-endpoints.html