As Kyle has mention above

 

 

putting an extra 8gb of ram ant going to help since fsx is only a 32 bit sytem and only uses about 3.5 gb of ram the other is used on other areas ofyour system. What will help is updating to a 64 bit system since you havnt mention if you have a 32 or 64 bit system. Try sliding down your all your sliders down than slowly increase 1by 1 to see when the freezes begin

It got a message from PMDG and they told me to run FSX with admin rights and now he saves everything! But now I have again the freezing problem

 

Now that I think about it...

It might help to grant full rights to your entire FSX directory.

 

I apologize for the self-quote, but I've typed this way too much in the past:

To do this, navigate to the Microsoft Games folder on your drive and:Right click on the Flight Simulator X folder:

Select Properties

Select the Security tab at the top

Click on the Users account in the Group box

In the Permissions box, check the box Full Control, Click OK.

 

This grants you (a User - Tron reference? ) and the programs you use in that folder admin rights to the folder. Essentially, what is happening is the computer is writing the changes (your key assignments) to a 'ghost' (Compatibility Files) folder, which the PMDG Options panel ignores the next time you run it. Using admin rights writes those changes to the actual file, not a file in a 'ghost' folder. As a quick note, if you have problems with any other program (especially when it comes to settings not saving, etc), you should grant admin rights to the program's location first before trying other things. UAC has its place in Windows, but it ends up being a bear if you don't know how to keep it in check.