Windows7 How to gather windows from secondary monitor

You can use keyboard shortcuts for window management. Use Alt + Tab to select the window that you want to move and then press Win + Shift + Left/Right to move from one monitor to another.

You may also want to try out Win + Left/Right/Up/Down

Got a solution.

I had the same problem using a C compiler, everytime I run an application, its text window was opened in the wrong place (the extended monitor).

Switch to the 'lost' window. Use any means to make it appear (one of the recipes commented in this page).

Right click on the upper left corner of the window to open the menu, OR press ALT+SPACE.

Chose 'properties'. Search in the menu for 'let the system position the window'. Check the option.

Voilà.

Sometimes when we disconnect the secondary monitor, We do not get all the windows tabs to our primary screen.

To get all those back to primary screen once you are no longer connected to secondary monitor, I have a workaround.
1-With WIN + P, try with computer only in projector option

If not solved Then

2-With WIN + P, select duplicate for projector option
And again With WIN + P, select computer only or Disconnect Projector option.

Hope this will solve your problem.