You have a 2 option to fix this issue either flashing the firmware or just reset the miner few times to solve this issue but you must reset the miner first before you flash it.
There is a 2 step that you can solve this issue.
- If you don't know how to do a factory reset you can follow the guide from Bitmain here
https://enforum.bitmain.com/bbs/topics/3957- If it doesn't work you can update the firmware with the latest version just download the firmware from Bitmain from here
https://service.bitmain.com/support/downloadIf still doesn't work check this troubleshooting guide from here
Possible problems and solutions for S7, S9 (fixed frequency) & L3+ 
