Try the bounding box collsioion detection!
Try this, it works for me every time. You can use this to make the ball bounce off of the paddles AND prevent it from going off the screen. I assume that you know how I got the ball.x and ball.y,
I just used a Public Type.
picball- is the picturebox on your form
paddle - is the paddle picturebox on your form.
If ball.x + picball.Width >= Paddle.Left And ball.x <= Paddle.Left + Paddle.Width And ball.y + picball.Height >= Paddle.Top And ball.y <= Paddle.Top + Paddle.Height Then ball.y = ball.y - 5
"ball.y = ball.y - 5" change this to ball.x= ball.x - 5 if your game is horizontal.
Hope this helps.