A small update now and summary, as this issue is still a problem but I have made 'progress'.
Summary
1) Pentaxforums is not down, site is accessible by others and me (in different ways)
2) Multiple browsers exhibit the same response (namely this error message);
3)
For a time, if I toggled between my Ethernet modem connection (adsl2+, TPG ISP provider) to my Optus 4GX Mobile Broadband USB connection (which is faster but limited data allowance) and still the issue persisted.
4) If I was on my Android tablet and using Wifi (adsl2+ home network), the problem persisted.
5) If i toggled firewall on or off, problem persisted.
6) I uninstalled wifi drivers, issue still present upon restart and win 10 autodetecting and adding wifi drivers back.
7) The only way up until about 30mins ago to even get on this site and make this thread was to use my windows phone, toggle wifi off and use its mobile data to gain access.
8)
The new development is I have somehow got my 4GX Optus Modem to now work with this site, this reply is being made on the PC using that network. All i did was unplug it, pull the battery out, give it 2-3 mins and then replug things back.
As it stands, if I toggle off my mobile broadband and back to TPG/Adsl2+ I still can't gain access to pentaxforums, from any device platform using that wifi. I'm still hesitant to believe this issue is my ISPs fault as for awhile Optus (the other ISP with the 4GX modem was also giving the same problem back).
I can't help feel this is an issue with the modem router, if there is a way to do a 'hard' reset (as I have tried multiple power downs). The fact the 4GX one started working again upon battery removal may be important?
FWIW I also installed chrome and added the 'nocoin' addon incase that helped at all (I thought i read Pentaxforums was perhaps subject to this
How To Stop Pirate Bay And Other Sites From Hijacking Your CPU To Mine Cryptocoins | Gizmodo Australia) (PS I don't torrent... at all.)