crossed off key display

That means that it can't see the key. Take a look at the battery in the remote as it's most likely dead

 

if everything worked fine, you might have a degraded 12 volt battery which will eventually need to be replaced.

 

You can check the key by how bright the red led is on the fob when you push the button. Take note of a freshly batteried fob how bright it is.

That and like Bisco said the 12 may be marginal. If the 12 gets really low it will throw a red momentary red exclamation point on the dash upon boot up. The red exclamation point is the only lamp that does not light upon boot up bulb check. It will if the 12 is below 11.4 volts under load. Thats the only warning you get the battery is ready to leave you.
Very noticeable.

Try this:

Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

You want the second and third number. Post it here.