Can't get to Mac OSX after installing Win7 with Bootcamp

I just installed Windows 7 using Bootcamp. Everything went fine until I had to restart the computer to finish the installation.

I think the mistake was that I pressed the ALT Key while restarting, because I thought the computer would maybe start with Mac OSX instead of Windows. So I chose the Windows partition in the Menu and hit Enter.

Now I have the problem, that many other also had. The Apple-SSD.sys file can’t be read.

I already googled for solutions for that and found a few, so this is not the problem.

My Problem is, everytime I restart my Mac it always starts Windows instead of Max OSX.

Pressing ALT-Key while restarting or something else doesn't work.

I tried pressing:

- ALT

- ALT+CMD+P+R

- C

- Z

- X

- Unplugged the Powercable to reset NVRAM

Nothing works! It always starts Windows and I end up at the Error-Screen...

Any Ideas what to do now?

Thanks in advance!