I'm afraid the advice given is very pertinent , do a search for the " 3 amigos " and then sit back and enjoy a long read , you will have to do what we all had to and familiarise yourself with the reasons that can cause failure because there are many.
I've just been through it and you'll need to apply a bit of logic to getting to the bottom of it.
Reasons range from the simple and relatively cheap to the not so simple and a bit less than cheap !
My advice is to get the codes read on the car and then take it from there .
For the record mine was the ABS pump .
Good luck.