The power failure  caused the mongodb server abnormal shutdown.Then it can not  startup,the wiredtiger file corrupted.

log as fellows:

1.unable to read root page from file:WiredTiger.wt:WT_ERROR :no-specific WiredTiger error

2.Wired Tiger has failed to open its meta data

3.This may be due to the database files being encrypted,being from an older or due to the corruption on disk 

4: You should confirm that you have opened the database with the correct options including all encryption and compression option.