i copied unreal from another computer but it download it and i already have it. it opens and start downloadin 4.5 GB and i already have it on my computer
Have you installed the epic launcher in the same place as the other computer and placed the engine files in the same place as the other computer as well?
google for UnrealRepair tool
Please take a look at this post. One of our Launcher devs (Swifty) is working with another user on a similar issue.
You can try the solutions provided already but if they do not work, please monitor the report until it resolves. Feel free to post a comment of your own to let them know another person is interested in this issue.