'05 Prius won't completely power up, but won't turn off

First, to shut the car off, hold in the power button for longer than 3 seconds. As to the problem of it not shutting off, it sounds like the combination meter is faulty. I'm sure others will chime in about whether the part would be covered under a recall or how to get it repaired.

 

There is a onboard test you can run on the 12 volt. I would do that rather than trust the test the other guy ran. No offense, but sometimes the tests run by mechanic's show the battery is good, but in a Prius you really need one that is not low on voltage. If you are seeing the red triangle momentarily when you power up, that is another indicator that the 12 volt is failing. Note I said momentarily (a few seconds)

Look in my signature file and click on the link that says test the 12 volt. Run the test after the Prius has set overnight and please post back all three readings.

I also agree it sounds like you might be having issues with the combination meter, but before I looked at that aspect I would test the 12 volt first. Easy test you can do on your own.

 

12v, unless yours is new,AgM and in good shape, that's what happens to me when. The 12 v is deded

 

My '04 did something similar, it would start and power up but would not get past the bulb check. After the bulb check, the MFD would have a mind of its own ( No avg. MPG or distance traveled). Had new battery installed, everything is back to normal. My mileage has improved also, my theory is that the charge circuit is always "ON" so it used more fuel to do it. Its just a theory, still love to drive this car almost ten years after purchasing it new. Plus, we got two more hybrids, '10 TCH and a '13 TCH. Nothing rides like a Camry, its a Prius Limo!