@jancef Oh, that's sad to hear. Does it do that same LED flashing sequence in any of the modes that can be selected via the mode switch? Can you check that the RESET button hasn't maybe got stuck...

@jancef Are you powering the router via the supplied power adapter or via the USB port of that laptop computer? It looks like the router is powering on and off over and over, like as if the supplied...

@Davide90 Does it force you to select an IP address or can you leave the "IP Address" field blank and only select a MAC Address and set Status to "Auto"?

@Ehsan0921 Could you post a screenshot of the configuration page here? (if there are usernames and passwords visible in the screenshot, then use a paint software to remove them)

@wgil It's hard to tell which device could be the source of the problem. As far as the router is concerned: In case your TL-WR841N is broadcasting on channels 12 or 13, try to set it to any channel...

@Mala116 If you want both routers to be in the same subnet and don't need any of the special router functions of your C6, then you could switch the C6 to "Access Point" mode and check if that works...