Breakout Collision Detection Algorithm Help

I'm having trouble with my breakout clone.

So far, for test purposes, I'm having the ball bounce off the boundaries of the window the game is played in (800 x 600). My current problem is that I can't get an effective boundary collision detection algorithm off the ground.

My main problem is that I'm stumped with an effective way to start the ball moving. I can get the ball moving however I can't adapt the direction for when it collides with the boundary of the room. For instance, to narrow down the problem, I have the ball inheritly moving in a diagonally left direction toward the almost top left corner of the window. When the ball hits the left boundary, if it's going in an upward direction, then the only thing that really needs to change is the x direction right? If this is the case, how would I correctly adapt the new numbers to the ball? This is where I'm stumped at.

If anyone can point me in the right direction, I'd greatly appreciate it. Thanks in advance.