one of the website hosted using ispconfig server is now showing a default page from pleak panel, which I never used. This problem is only when I am trying to access the site without the www i.e. domain.tld or http://domain.tld, but if I am using www.domain.tld, it is opening perfectly. other sites on the same server are working fine. Please help, what I should look for. where can be the problem. is it hacked?
I dont think that you site has been hacked. I guess you have just a wrong dns record for domain.tld while it is correct for www.domain.tld. Check the dns A-records for domain.tld and www.domain.tld and make sure that both records point to the IP address of your server and not any other server.
Yes, you are right, I am facing this problem just from one PC, from I can access the same alright from other places. This is a strange problem, can't figure it out?