SSH working, Panel & Websites don't

[theomidm]

Hi,
i have a weird problem, every thing was working great. but today when i tried to access the panel, i couldn't, it gives unknown host error when i ping it and it gives nothing when i try to open it with browser.
then i checked all websites and they didn't work too.
but i can SSH, and when i try to access panel with ip instead of domain, i can.
what is the problem?

[tjebbeke]

DNS server down? try to run v-list-sys-services and check if there is some service not running.