Hello PabloIaCo,
Thanks for reaching out to Microsoft Community. I'm sorry to hear about this issue on your device and external monitor. I understand how frustrating it is to have such issue. I'll do my best to help.
If I may ask, what version and edition of Windows your device is running?
What is the make and model of your external monitor?
Were you using a Surface dock to connect to the external monitor?
In the meantime, since you haven't done any troubleshooting yet, I want you to follow the methods from Troubleshoot connecting Surface to a second screen (microsoft.com) to troubleshoot your device.
Then, let me know how it goes. I'll wait for your response.
Regards,
StevenK