Why different nslookup results?

Question

Domain Name System

Something incomprehensible has been going on in the enterprise network since yesterday.
first of all - sites do not open, browsers swear at dns.
the local stopped processing requests. I plan to reconfigure in the evening (win2008).
Well, in dhcp I specify that everyone would have dns 8.8.8.8 (network without a domain).
Some sites start working immediately, but they open halfway. For example, images do not open on habré, although habrastorage.org is available and pinged, css is also not loaded, sites are sprawling.
But something else is strange: I run nslookup on computers, point it to 8.8.8.8 with my hands - but it still does not see some domain names, for example, lenta.ru does not resolve. Well, I ran through the major sites of the Runet - the same thing, some of the domains do not work.
I go to a remote server and there, of course, they completely resolve and all that ...
Kaspersky is installed, which is completely updated. I don't think about viruses.
But the problem is unclear where buried. For some reason, the internal dns also stopped working, didn't it?
Internet is served by a twisted pair cable, then there is a router that raises the pppoe, then a computer with a TrafficInspector.