Try at a lower baud rate (like 9600 Baud) and if that doesn't work see if GPIO0, GPIO2 and GPIO15 are as they should ("UART-mode" when flashing):
Try at a lower baud rate (like 9600 Baud) and if that doesn't work see if GPIO0, GPIO2 and GPIO15 are as they should ("UART-mode" when flashing):