Have you tried to delay the loading of the current sketch by the processor and uploading basic sketch like Blink? This can be done by pressing the Reset button twice quickly. This puts the chip in bootloader mode for 8 seconds during which you can attempt to upload the Blink sketch. If this works, try uploading your code. If your sketch stops turning on and off, you should be good to go. If it doesn't, repeat the reset process and look your sketch over, there is something in it that is causing the reboot.