I just upgrades my routers OS to 6.18 and I can access it through winbox, but I cannot for the life of me get my wireless to broadcast anymore. Please help, or if possible please tell me how to revert back to older OS versions.
Router is Groove a-2hn

Thank you!

Put the wanted packages of desired old version into files and then press downgrade button in system / packages.
But I would try to find the reason before, if not found, netinstall of the newest version and after that I would downgrade (rather by netinstall too).

reset your wireless interface.
then reboot
have you updated routerboards firmware?

I had the same problem on a RB711.
After reseting the wireless twice and rebooting it came back