A domain can only point at one place for each record. If there is already an A record on @ pointing at your old host, and you add another pointing at us, your registrar now has two conflicting instructions and will keep serving one of them, usually the old one.
This is the most common domain problem after ordinary waiting, and it is nearly always a leftover from when the domain was bought. Registrars often add their own record so a freshly bought domain shows a "coming soon" page rather than an error. That record is still there, quietly winning.
Do not touch MX or TXT. MX records carry your email. TXT records prove you own the domain to services like Google and Xero. Neither has anything to do with your website, and both should be left exactly as they are.
Step by step
Go back to your registrar DNS settings.
Look for any OTHER A record on @ , and any other CNAME on www.
Delete those, keeping only the records Kitset gave you.
Leave every MX and TXT record exactly where it is.
Save, then press Check now again.
If it does not go to plan
There is a "parked" or "under construction" page.
That is your registrar serving its own placeholder, because of a record they added when you bought the domain. Removing that record is the fix.
I deleted something and my email stopped.
Put back any record whose type is MX. If you are not sure what it was, your email provider can tell you, and so can we if you say who hosts your email.
I cannot find any conflicting record.
Send us a screenshot of your DNS settings with the domain visible. This is usually settled in one reply.