Why my car turns off ?????

Last week my car didn't start because it had a blown gasket due to heating. Got it replaced today , and out of the workshop , i found that my car did not accelerate as before , i.e it takes a bit time to power up above 1500 Rpm and then goes fine. Also when idle, the rpm goes below 1000 and rises a bit but when lowered it kinda starts to stall. While i exited a highway to a local road today , when i braked while i was on 4th gear , the car went off before I could press the clutch !! And then the steering wont move and cannot press the brakes too !!! I had to catch the hand brake to stop the car....,what actually is the problem. Thanks for any help !