www.domain.tld works but domain.tld doesn't

[Been Told]

I installed ISPConfig2 on Debian Lenny (according to Howtoforge tutorial) and I'm having a little problem.

I added a Site and set up the records. But for some reason www.domain.tld brings up with the usual ISPConfig standard page, but domain.tld does not.

Can someone tell me what I'm doing wrong?

[till]

Add a co-domain domain.tld with empty host field.

[Been Told]

The only domain in the "Co-Domains" Tab is already without a host.

[till]

Then the dns A-Record fo domain.com might be missing.

[Been Told]

No, it's not that either.
I have an A record with www one without a host and one with mail.

So:
domain.tld
www.domain.tld
mail.domain.tld

[Been Told]

I've just realized... It was a problem with the nameservers I've set up.
I'm using a Hetzner server. Now I've switched to Hetzner's nameservers, it's working with and without www.

So now I'm gonna have to figure that out. Thanks for trying to help guys.