One more thing to try:
A discharged or defective 12-volt battery can sometimes cause odd failure symptoms.
Connect a known-good, fully charged, 12-volt auto battery in parallel to the 12-volt battery in your Prius, like you were going to jump start a regular car.
Then, turn the Prius ignition on, check the display, noting what you see (so that you can later post that info on this Website), and see if you can start your car.
If that doesn't work, or give you more and/or different failure symptoms, your high-voltage traction battery may be discharged. If that's the case, your dealer will have to charge it for you. This requires a special Toyota charger designed for your hybrid battery, and it is unavailable elsewhere. In fact, a discharged traction battery is so rare that most dealers do NOT have one on site; and they usually have to have it shipped to them. So, I'd plan on your Prius being in the shop for a few days, assuming that this is the problem.
Unfortunately, that is about the extent of my troubleshooting experience as another Prius owner. And, it appears that most of the other members on this site are either not following this thread or haven't checked this site recently. However, if I didn't mention it already, you may want to check on other, more active, Prius forums to see if one of their members has experienced similar problems. The one below is probably as good as any to start:
http://www.priuschat.com
In any case, if this was my Prius, I would think it's time to take it to the local Toyota service department for troubleshooting. There are not many other alternatives for hybrid owners.
Good luck!