found the Brake & the ABS lights on after picking up my car from being parked for 3 weeks

1. I suggest that you fully-charge the 12V battery. You need to hook up a charger, 4A charging rate, and leave it overnight. Do not underestimate the time needed to charge the battery.
2. Make the Prius READY and open the hood. Look at the inverter coolant reservoir and you should see turbulence in the fluid within. This shows the inverter coolant pump is running. The pump is located directly behind the driver's side headlight assembly. If you don't see turbulence, the pump has died and that is the root cause of your car's problems.
3. After the battery has been charged and you have confirmed the inverter coolant pump is running, if the warning lights remain on, then you can either visit your local Toyota dealer for help, or else buy Mini VCI which runs on a Windows XP or Windows 7, 32 bit OS laptop to retrieve the diagnostic trouble codes. Those are needed to determine what is wrong with your braking system.

 

12 volt battery?

 

if it was me, first I'd check the brake fluid level, top it off if needed. then pull codes. then I would disconnect the 12v battery for a couple minutes to see if the codes will clear.

 

All of the above.
How old is the 12 V battery ?
If it is original, you are definitely due for a new one.
If it is more than 4 years old.....probably.

Then.....it is possible that a wheel speed sensor went bad while it was sitting there.......or a corroded connector for same finally failed.

 

On a Gen2 sitting three weeks its a good idea to turn off the smart key system (button under the steering wheel). Otherwise the 12v battery can get drained that may cause funny things like you see. It's hard to re-charge the 12v battery driving locally as takes a long trip to really charge it back up. That's why you are getting some of the recommendations above re: 12v battery.

 

I've taken 2 trips to china for 3 weeks each time and never had a problem. but it could just be a weak battery, especially if its the original.

 

Well, I just took my car to the dealership, and the diagnostic was low pressure in the break line on the rear right side.
So they had to flush the brake lines and all of that ended up costing me $240! Urgh...
A few months prior, I got brand-new brakes, I thought this would've been detected then. But what do I know about cars? :-D

Sorry, seems like I have 2 different IDs... Same as Adiva45 above...

 

oh! i was wondering. they probably did your discs and or drums, but not the brake fluid. your driving an 11 year old car with how many miles? you're going to have to start expecting stuff.

 

you don't want 11 year old brake fluid in your car anyway. money well spent.