I'm trying to help out a friend with this issue; the computer in question is not very old; it was new in November 2014.
The issue seems to be that some websites become inaccessible in both Internet Explorer and FireFox; what happens is either the page tries to load and simply never does without displaying an error or sometimes you get "this page cannot be displayed".
I set this computer up for them and it has Eset Endpoint 5.0.2237.0, Malwarebytes and Spybot 2.4 installed. Despite the problem with web pages, the anti-virus is receiving regular updates and you see the notification balloon at least a couple times a day that the definition database was updated.
Initially when I started looking into this, I did a full system in-depth scan with Eset and it turned up a few minor things but nothing serious; I tried to update Malwarebytes Anti-Malware and Spybot and Spybot encountered errors during the update but by clicking update several times it was finally able to complete all updates. On the other hand Malwarebytes was never able to update.
I tried resetting TCP/IP using "netsh int ip reset" in a command prompt running as administrator and after a reboot things seemed to be working fine again; I was able to update Malwarebytes and scan with it but it only turned up some tracking cookies.
I tried downloading and running TDS Killer 18.104.22.168 and it didn't find any problems.
Things continued to work fine for a day or two and then the same problem started again.
Just fyi, my friend has their home wired (this problem computer is attached by wire) and they have a wireless router and every other computer (there are at least 5 not counting this one) on the network works fine and it's only this computer that appears to have a problem.
Does anyone have an idea how to permanently fix this problem?