Hello,
Is this an issue with a single device or several devices?
Was the power outage a regular or something out of ordinary with possible voltage or current spikes, able to damage the device?
Did you have any complex configurations on the router?
What services have you had running on the device at the time?
Did you have remote HTTP(S) or SSH access enabled on standard ports of the device?
It is always suggested to use latest firmware, thus, in any case, I suggest to download it from here, and, independent of the currently installed version, update it with Keep settings option disabled. Keep in mind that this will erase your configuration, but, if the difference between firmwares is more than two iterations, will help to avoid possible errors and malfunctions caused by migration.
Best regards,