DaemonUmbra

1.8 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Try running the jar from the command line as shown in this video:

1.7 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Ding doesn't work on a server, remove it

Please provide debug.log (more info on where it is and how to provide it in my signature below, just expand the spoiler)

Not according to the log you provided, please provide debug.log

If you are referring to ComputerCraft, the original has been retired but CC:Tweaked is a modern fork of it. However if you're talking about schools then unfortunately they may also be using ComputerCraftEdu, which hasn't been updated.

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

I've seen people say that allowing Java through their firewall worked.

Please provide debug.log (more info on where it is and how to provide it in my signature below, just expand the spoiler)

1.7 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

We don't support 1.7 anymore because it's ancient (6 years 5 months old). Sorry. Ask the organizers how to fix this and tell them we recommend updating to modern versions.

Show a screenshot of the file you downloaded?

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Please provide debug.log (more info on where it is and how to provide it in my signature below, just expand the spoiler)

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Really old Minecraft versions are no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Did you try installing the mod that provides it? https://www.curseforge.com/minecraft/mc-mods/scalable-cats-force

Are there any hs_err_pidXXXXX files that have appeared?

What version of Minecraft are you using?

1.12 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

1.7 is no longer supported on this forum. Please update to a modern version of Minecraft to receive support.

Just realized I had mistaken the name of a graphics library to be the name of a pirate launcher, sorry. Can you restart your launcher and try to run the game, then close the launcher and provide launcher_log.txt from .minecraft?