The way to fix the issue is as follows:
1) connect Ethernet wire to your laptop and any of the 12 ports of 7150
2) Make sure your router is connected to 7150 as well
3) from windows machine open command prompt
— in start menu, search for cmd and you will find it
4) type arp -a and press enter
5) you will see list of IPs starting with 192; one for the router and one for the switch
6) ping the IP of your switch through a web browser; it usually is the second one
7) it will direct you to unleashed.ruckuswireless.com
8) enter your unleashed username and password
9) and now you are all set to manage your network again; you will see WLAN option to enable again