Not connecting to 5g, even open

[pplui]

I am having troubles with my ac3100

I was loosing connections, or connected with no internet, so I reset it by hard reset , software and WPS.

Also, I downgraded to stock firmware using recovery mode, and tested several other merlin versions ( always resetting everything)

I have no problem with 2.4g, but I can not connect at 5.0g, even if I leave it open .
The problem is in android,iPhone and windows

Another interesting fact is that of I try to connect in windows, when I enter a intentionally wrong password the answer is always " can't connect to the network" regardless of the password error.

What can I do?

 

[wouterv]

Guideline in case of unexplained router behavior:

1. If there are, disconnect all USB devices.
2. Install the latest available firmware version.
3. Reset to factory defaults.
4. Do not load an old configuration backup file.
5. Manual configure the router with the bare minimum, as:
   • Router Login Name.
   • Router Login Password.
   • WAN Connection Type, and what is required to connect to the Internet.
   • Wireless SSID's (use only Aa to Zz and 0 to 9, no spaces and no odd characters).
   • WPA Pre-Shared Key's.
   • Leave everything else default.
6. Test the router behavior:
   1. Test with a wired connection first.
   2. Test with a wireless connection at an unobstructed distance of about 3 meters.
7. After the above works all well you can consider more manual router configuration changes.

Notes to the above guideline:

• For the WAN connection and wired LAN connections verify that the port speeds are sufficient (1 Gbps or even 2.5 Gbps).
• For wireless connections verify the Tx rate and Rx rate.
• Restoring a configuration backup might bring back old issues, that is why the manual configuration is advised.
• While making configuration changes: write them down so you do have a list of changes you made from factory defaults.
• Whenever you restore a configuration backup: only restore the backup to exactly the same firmware branch and version as it was made with.