In certain instances, the 737 load manager may not work in Windows Vista or Windows 7. The sliders won't move and the boxes are all zeroed out.
The root cause here is file permissions - the 737 and FS9 itself were both created long before Vista and Win 7 existed. These OSes drastically changed how the "rights" of users logged onto the system work. The problem happens when the system thinks for whatever reason that the load manager's exe doesn't have the necessary rights to write to other files - namely the loadmanager.ini file and the aircraft.cfg files that it needs to be able to edit and write to.
Here are the steps to fix the issue:
1. Download Flight 1's Registry Repair Tool found here:
http://www.flight1.com/view.asp?page=library
Run it -
IMPORTANT: make sure you right click and choose Run As Administrator - select the FS9 option. Then, browse to your FS9 root folder and select the main exe file (either FS9.exe or FSX.exe) and press open.
This is making sure the registry entries are correct, which can also play into this problem.
2. Download "TakeOwnership.zip" from this website:
http://www.howtogeek.com/howto/windows-vista/add-take-ownership-to-explorer-right-click-menu-in-vista/
Extract it to your desktop and double click the "InstallTakeOwnership.reg" file. This adds information to the Windows registry that will create a new option in your right click menu that allows you to easily assign full control of files and folders to your Windows user account.
3. Using Windows Explorer or My Computer, locate your root FS9 folder, right click it and select the new "Take Ownership" option - a DOS-style terminal window will appear and you will see it run batched permissions commands for several minutes. Wait for this to finish.
4. Navigate to your FS9\PMDG folder - right click on the "LoadManager_FS2004.exe" file. Select Properties at the bottom, then select the compatibility tab. Place a check mark in the bottom option, "Run this program as an administrator".
5. Double click the "RemoveTakeOwnership.reg" file if you wish to get rid of the right click menu option.
The problem should now be solved and the load manager should work.