Killed Gt2560 after failed marlin upload?

[Melita01]

Hello Guys,

i kind of killed my board. Firmware upload failed and after that i couldnt upload any marlin anymore.
https://snaptube.cam/
Tried to flash a new bootloader with my usbasp and it finished the upload successfully. After that i still cant upload marlin via usb cable and if i try to upload marlin via usbasp programmer i get at the end the error that the port is not available. It finishes, but shows after all an mismatch error.

I tried to use an arduino nano as a isp flasher, but if i connect the gt2560 i get an error.

Is something burned on the board? maybe usb- connection somehow?