It's impossible to see what is the reason of this issue. Something conflicts with wpForo so please deactivate all plugins and check it. If the issue is fixed, activate the plugins one by one and check after each plugin activation to find the conflict maker.

@joselito,

Have you contacted with your host support?

Posted by: @joselito

I've tried without cloudflare and nothing changes. :(

Then i have no idea, maybe ask your hoster for help.

Posted by: @joselito

Posted by: @dimalifragis

@joselito So this is a server or webserver/nginx issue. OR due to Cloudflare.

This is what i found searching the internet, since i have never seen that error before (and i have seen a LOT).

Could be cloudflare, mmmm...but CDN is important, should I disable it?

Disable it for a while. Just to test.

@joselito So this is a server or webserver/nginx issue. OR due to Cloudflare.

This is what i found searching the internet, since i have never seen that error before (and i have seen a LOT).

Do you have disk space left, could your disk allowence be full? And also are you on nginx web server?

@joselito 

When in Wordpress Dashboard, press F12 and click on your browser Console.

In there you will see any errors.

Then goto to forum and plugins dashbards and see the errors and post them here.

Pictures attached 1

Videos

Advanced attachments addon panel don't work

https://youtu.be/sM-XDa2YuQY

Forum dashboard don't work

https://youtu.be/ecNOPjEVmkQ

Other addons panels work nicely

https://youtu.be/3foAlMXzbR8

Kyle from gvectors is telling me to fix console errors but I don't know what errors he's talking about.

@joselito,

It seems your addons were not updated.

Please delete addon folders using some FTP client or the File manager of your Hosting cPanel, the addons folders are located in /wp-content/plugins/ admin page. This will fix the site access issue. Then install the new ones.

If you also have installed an old migration tool coled go2wpforo then delete it as well. The folder name will be the same.

Then download and install the latest 3.0.x  versions of addons from your account page: https://gvectors.com/my-account/

This happened before the update to wpforo 2.0.

My addons are updated to 3.0, do I have to delete them and reinstall? ? 

Here's a cap of my plugins folder.

What "i can't access the dashboard" means exactly? Is there an error? A timeout? An error in browser console (F12)?

There must be something. In debug . log maybe?