Windows 7 - Cannot make external display my main display

Set-up:
Asus x51r
Samsung BX2250 - external monitor
Windows 7

1. External monitor is detected, can only extend monitor.

2.1. On Screen Resolution Menu:
When I put a check on "Make this monitor as my main display", it shows "cannot save display settings".
2.2. Only 2 options appear on Monitor 2 Multiple Settings:
A. Disconnect display
B. Extend this display

3. on Windows Mobility: when disconnect display is clicked, no response, but it shows that Monitor 2 is connected.

4. Windows+P not functioning as a shortcut but the rest are.

I have uninstalled/re-installed, updated drivers, restarted laptop more than 20 times. Asus x51r has ATI Radeon Xpress 1100.
Everything was fine when I was with Windows XP. Also, the Switch Monitor Fn Key on laptop doesn't seem to work after I installed Windows 7.

Any insights on how to deal with this? Thanks!