A number of users have reported being unable to connect to Discord from their school internet service. We believe a vendor used by multiple campus IT departments may have blocked access to discord.com.
We're investigating the cause and solutions, and will update as we learn more.
Here is a possible fix, so long as you are complying with the requirements set by your network admin:
Update your DNS server address in Network Settings to "188.8.131.52" (Google's Public DNS), or "184.108.40.206." (Cloudflare's DNS)