Apex domains cannot have CNAME records.
Question and response
Question
dig s4-power.com. NS
Answer
s4-power.com. 5 NS ns-1908.awsdns-46.co.uk.
s4-power.com. 5 NS ns-165.awsdns-20.com.
s4-power.com. 5 NS ns-1468.awsdns-55.org.
s4-power.com. 5 NS ns-1970.awsdns-54.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0