First of all, you could thank the developer called spavlin for their great ROM.
You can not get new user and complain about their bad experience, no one forces you to break your device it is always at your own risk.
Thank instead of getting angry, because your device is already long dead and Samsung's fault.
Do the following:
1 Download the desired firmware and unzip
2 Download SMD Downloader v3.47
3 SMD Downloader v3.47 starting the program in the yellow folder opens the ROM .WP8
4 In the green folder opens the SPV doc.mbn
5 Turn off the device and turn it into Download Mode and connects the device to the PC and press start in the SMD Downloader v3.47 program and wait for the device to complete the process and restart.
6 After the end of the process the device will reboot and enter loop restarts. Do not worry, disconnect the USB cable and remove the battery from the de vice.
7 Replace the battery and enter back into the Download Mode.
8 SMD Downloader v3.47 We close the program and start again. Now the yellow folder and select the file named #MassStorage or # MassStorage2 you click on Open. Now on the right side where it says "DL option" brands "Select".
9 Connect your Samsung ATIV again to the USB port and once the program detects only have to press Start. Now visualize a mistake, do not worry click OK or ACEPTED
10 When completed, the Samsung ATIV S will restart and you can disconnect the USB cable. Now you wait a minute and see that there will loop of restarts and finally load Windows 10 Mobile.
11 Factory Reset your device by combining keys.
PS: you have to acknowledge the help both the ROM developer. as others for help. If you have trouble following the steps, then the problem is your device that is dead forever.
Sorry for my bad English but using Google translator because I'm Spanish
Thank you very much for contributing to his rom spavlin for the device, it is a great effort and I appreciate it greatly. A hug champion