Can't visit certain websites?

Ever since last night, I've been unable to view a certain site (gpxplus.net, an adoptables site) through my Wi-Fi. I've checked that the website has been up, and neither my PC, IPhone, or a family member's laptop can access the site. I've tried using FireFox, Opera, and IE to get to the site but with no luck. All times I've tried, I've gotten errors such as "Can't Connect To Servers" and along those lines.

I've tried several options (Changing DNS file/server, changing IP address, restoring browsers to factory settings, ect. Basically the common solutions). I've only been able to access the site through mobile data or proxy server.

I haven't been able to find much else on the subject, and I've grown tired of searching and failing to fix the problem. Does anyone have any ideas?

Added (1). Unfortunately, it appears that the firewall and host file solutions do not work. Ughgu.

Basically there are to reason for this kind of problem:
1- Your firewall is blocking that website
2- You need to edit your host file, because there are additional strings which.

The first case is simpler, because you need to remove the rule from your firewall.
The second may be tricky. You have to navigate to C:\Windows\System32\Drivers\etc and open up the host with notepad. If you see that there are strings regarding this website, you must cut them off.