Hi guys. I'm new to the forum and have found this thread via Google as I had the exact same issue but I have now resolved it.
My Hikvision DS-2CD2032-I has been working perfectly for around 12 months now on HTTP port 8008 but last night it stopped responding to everything and a ping of the camera was intermittent (I got several good pings then it would stop responding then come back etc.) I couldn't get access to the camera via HTTP, HTTPS, RTSP, nothing. I reset the camera and went back in via the default IP on Port 80. No problem. Change the port to 8008 and it stops. This happened several times.
To cut a long story short, it seems my ISP (Sky in the UK) has upgraded the firmware in my ADSL 2+ modem router overnight and has added new features, one of which is WAN and LAN side IPv6 which was enabled. I disabled IPv6 and the camera now works perfectly again on 8008.
Hope this helps you guys.
Cheers,
Rup