Keyless Entry FOB not working

Check the button on the lower part of the front dash. It may have gotten bumped. It turns the keyless entry off and on.

 

if that's not it, check the buttons on the fob, make sure none are stuck in the depressed position. then move on to the 12 volt battery. all the best!

 

If you have Smart Key and the remote battery dies, it won't unlock the car, but if you put the key in the key slot it will still start the car. Didn't see if you checked the Smart Key button below steering wheel and if that fixed the problem.
Here is how to change the remote battery on the 2007 Prius.
Replacing the Wireless Remote Battery-CR2032
I've included the page from the Owner's Manual, but my steps are numbered slightly differently.

1. Remove the mechanical valet metal key from the side of key remote;
2. Remove the emblem cover while sliding the lock knob on the end in the arrow direction.
3. Remove the 4 screws to take out the metal lid off the module.
4. Remove the discharged battery and put in a new battery with positive (+) side up.
5.Install the lid with the 4 screws.
6.Replace the emblem cover and the mechanical key while sliding the lock knob.

After replacing the battery, check that the key operates properly. If the key still does not operate properly, the comment about the 12-volt is next suspect. It can cause a myriad of quirks.

 

The button is below the steering wheel column, and says "KEY" on the label.

 

Here are Drawings of two switches you may have under your Steering Wheel, the Smart Key Activation Switch and the Tire Pressure Warning Reset Switch.

 

If the little red light just to the right of the of the "Lock" button on your fob lights up bright when you push any button they there is nothing wrong with the buttons on the fob. If one of the buttons was sticking on (the most common failure of the fob buttons) the light would not light up at all. If the light is dim when you push a button on the fob then there may not be enough signal power from the fob to be received by the car. I sometimes have a problem with my iPhone being too close to the fob and it interferes with the signal, since my fob is in a pouch on my belt, right next to the iPhone (I have to make sure they are separated by a few inches so the fob works). I also have some problems when I am too close to the Navy bases around here due to some frequency they sometime use, but that is mostly with the fob for my Harley Davidson motorcycle. If the light is bright when you push a button then I would check the 12V battery. Mine went dead a couple years ago and I just went to the Toyota dealer and bought the standard one they sell for it. It was cheaper, in cost, then a regular battery for a larger car. I think it cost about the same as the one for my motorcycle. Oh, yeah, make sure the contacts for the fob battery are pushing up on the battery so that the top you screw back on after putting it in has to be held down until you get at least a coupe of the 4 screws back in. If not just slightly bend the two battery contacts in the middle of the battery area up some, this will make sure there is good contact on the fobs battery connectors. Hope something in the helps, good luck. oops, just noticed how long ago the last post before this one was, probably found what the problems was by now, I hope. If so, NEVER MIND.