I am new to staredit so I dont know very well how to use triggers.
I made a custom map, put 4 players on it, gave them buildings and put to 3 of them run ai script custom level, and after that I tried campaign difficult
but none of them worked. Computer just seemed to do nothing but mining, and scatter some drones/probes on the map patrolling.
What can I do to have a fighting computer, building base and attack me?

Wrong forum, so I've moved it for you

On your question:
I am not an expert for SC1's AI, but here is a list which might help you: http://www.staredit.net/starcraft/List_of_campaign_AI_scripts

That list of scripts does not really help , i just want to make computer play like in melee map ; building up and attacking.

It does help if you want to customize your enemy.

However, the script is working for me, by using Condition: Always, Action: Run AI Script (at location) [it does not matter if you run it in a location or not, both work (at least in this example)]

I've tested: Protoss Campaign Insane and it is working flawless.
Further testings show: if the race of that computer is not protoss, it will do nothing but mine minerals.

I've attached my small test map.
Change blue's race to something different and it will only mine.

Attachments:

It worked, the protoss did as it should. But my problem seemed to be that when i check run ai script there was no script available except send troops on suicide issions,
so i tried run ai script at location where location was anywhere and this was the error.
Now i set the locations 0, 1, 2 ... and the scripts campaign insane works fine for all 3 players.
Thank you very much anyway.

I might be wrong, but the ai scripts not being listed-issue sounds like you are using StarEdit (default editor).
For more flexibility, more features, make sure to give SCMDraft a chance.

I tried scm draft 2 and it is a lot better tha the default editor, thanks.