Hard brake pedal on AUDI A3 8PA 2.0 TDI AUDI A3 Sportback (8PA)

Hi All 

Just wanted to see if any of you have some sort of diagnosis for a problem on my 2006 AUDI A3 2.O TDI.

One day whilst I was driving my car and coming up to some give way markings wanting to join the main road I went to press my brake pedal to stop when suddenly the pedal went rock hard and the car would no longer stop. This resulted in me being in first accident as I collided with another vehicle when coming out. 

I understand when the car is off and I pump the brake pedal it should go rock hard but when I turn the engine on I am able to apply good pressure to the brake pedal. 

However I don’t understand why it would go rock hard whilst the car is on. Checked brake fluid which is fine front pads have got plenty of life rear pads less but still usable. 

The one thing I do recall is the whenever I am going above 50 mph or could just be generally at any moment my handbrake light flashes on the dash and I hear 3 beeps. Not sure if this relates to it any way but i’ve had this handbrake light for a while now.

Ever since the accident i’ve had a really inconsistent brake pedal, sometimes hard to push sometimes easy to push. 

Any sort of advice or help would be greatly appreciated.

Many thanks.