The STARTUP2 state means the node cannot vote. A member of a RS enters this state once the MongoD process completes loading it's configuration. In this state, the member has created threads to handle the internal replication operations but it has yet to change state to Recovering and onwards from that to Secondary (see the [state and their details in the docs]).
If your node has been in this state for more than a brief period then you are encountering some strange behaviour. This is pretty much impossible to analyse without the logs to determine why it is stuck. Running rs.status() and db.printSlaveReplicationInfo() will give you some details on the local picture on the node.
The normal approach to resolve this would be to shutdown the node, wipe its data files (those files in the dbpath), and restart it. This will restart the initial sync process and it should move to SECONDARY. If it gets stuck in STARTUP2 again, you'll need to look at the logs to gather more information as to why - there are a range of causes but one that can happen is a flaky network or some local resource contention.