The screen got  stucked at firmware update and doesn't  do anything. Is there a way to do a hard reset?
Or can i connect it with pc because i've tried two smartphones, they connect but  nothing else.

Hi, IanG90. Thank you for reaching out. You can only update it through the DJI Ronin app. Please follow the steps below to update the firmware:

1. Press and hold the power button to power the gimbal.
2. Launch the Ronin app, tap Connect to Gimbal, and select your RS 3 Mini on the device list.
3. When new firmware is available, there will be a prompt on the top of the Ronin app main page that says "Update Now."* Simply tap it. There will be a prompt to indicate a successful update. Tap Exit to complete the update.
4. If the update fails, restart the device and try again.

Notes:  
1. Before updating the firmware, make sure that the gimbal battery is fully charged.  
2. When updating using the Ronin App, make sure that your mobile device gets access to the Internet smoothly.  
3. Do not turn off the gimbal during a firmware update.
4. If the update fails, restart the gimbal and try again.

After a lot of tries i've updated it, but after i reopen the gimbal it  asks me to update it again.

IanG90 Posted at 10-27 09:19
After a lot of tries i've updated it, but after i reopen the gimbal it  asks me to update it again.

Hi there. We're sorry for the trouble. I'm afraid that you may consider sending the unit in for a proper diagnosis. You may contact our support team to start up a ticket at https://www.dji.com/support or contact the dealer where you purchased the product to check their after-sales services. Thank you for your understanding and support.