This thread is related to things you can try/attempt to try before making a thread in the Help section. I'm going to extend on the 4 points that Cyk753's thread (which can be found here) has stated, as well as suggest many more possible fixes.

Firstly, if you can't start your game at all, make sure you have Java installed in the first place. This is sometimes due to the fact that Minecraft may not have all the libraries required to start - an extremely unique issue, as usually the Minecraft Launcher installs all of the libraries required when you install the launcher or launch the game for the first time.
https://java.com/en/download/

With the most obvious 2 fixes out of the way, I will extend to slightly more obvious or uncommon errors.

If problems persist, a Google search will always help, or by posting a thread in the Help category of the forums, linked below.
Help | Skyblock Official Site

 

This is quite informative, thank you for making this thread!!

 

Really detailed thread with different alternatives!! Appreciate it, thank you

 

Installing Java is useless, if you don’t have it, Minecraft will automatically download it for you

 

reinstalling java has fixed issues for me in the past, especially with Forge/Optifine.

 

Updated the "I went to classic, now I can't connect! (long Loading Terrain time then disconnecting)" section to include a small step by step on how to change version.

Also added a line in the "IP Blocked!" section to include going to the SB Discord for further help.

 

thank u pc

 

Updated this guide to be more in-line with today's connection issues. Also servers as a bump.

Changelog:
- Changed the description of installing Java to provide more reason as to why installing Java before you play Minecraft: Java Edition is a good idea. Fairly self-explanatory.
- Edited the server versions for the "Visual Bugs or weird protocol errors" as this hadn't been changed since the server was on 1.12.2.
- Edited the "Using an alt account manager?" section of the Invalid Session section as most alt-managers on clients are redundant due to the change to Microsoft accounts. im still upset about this
- Changed the Bedrock section as it was old, and that Skyblock now has a GeyserMC proxy directly set up to allow for bedrock connections.
- Minor typo and formatting fixes.

Still need to fix all the broken embeds, however should be fairly straight forward for the less complicated fixes.
fixed