I'm stuck

system just keeps repeating this and won't let me do anything:

-zsh: fork failed: resource temporarily unavailable

I would appreciat any help. Thank you

Sounds like you have a process that is eating up all your memory. You should reboot the system, then if it happens again, make a careful note of what was running right before this message started appearing.

Well I'm connected to a unix server of my Internet provider.
How do I reboot that ?

In that case you should probably report it to your ISP. They should be able to take care of it.