device not working after installing 7.6

hAP ac2, use WebFig to upgrade to latest version 7 release.
After restart, the device is obviously not working. LED for connected ports blink, after a while, LEDs on all port light at the same time. Again and again.
And the device does not show up in Neighbors in Winbox v3.37.

How can I do to get the device work again?

Netinstall.
And latest release (stable) is 7.8.