During upgrade, my E1550 cannot startup correctly. If not run tftp, the router will response ttl=100 for 5~7 seconds, then no response. If run tftp upgrade with official firmware, the transfer completed successfully. But router won't boot up after transfer. and response ttl=100 forever. I know ttl=64 means there is OS in the device, so seems OS cannot be loaded for my device. If there any additional steps I can use to active my device? Thanks in advanced for your help.