@tony0211 After you updated the router firmware, did you reset it to factory defaults, then reconfigure it from scratch? If not, give it a go. One more thing, are all the devices disconnecting from...

@Abid12 May I know your TP-Link account? If you have already changed the username and password, please ensure you typed them in correctly. If possible, try with another phone and see how it goes....

@SeByDocKy What is the symptom of the crash? Please try to describe the LEDs status when it crashed, can you see its wireless network when it crashed? You can try to reset it to factory defaults...

@Jeweljene Please refer to the below FAQ to do some basic troubleshooting if the speed is not good when connected to the router network: https://www.tp-link.com/support/faq/2170/

@TL-WR840NNN If the speed is slow when connecting to the WR840N, please verify which case are you belonging to: https://www.tp-link.com/support/faq/2170/

@Arun223 The Archer C50 has 100mbps WAN/LAN ports, that is going to be a bottleneck for you, it would be better to upgrade to something with a 1GB port if you get a speed of 300Mbps.