When I open a second window, the first slides off the screen.

Are you referring to Mission Control and several different desktop images

you can move around in there? You can control items via Launchpad, too.

•Mac Basics: Mission Control

http://support.apple.com/kb/HT4689

Do you have more than a few open applications? That is where Launchpad

can be either a blessing, or a curse. They are part of your multiple desktop

images, if they are open. Some of the settings affect other visual access.

•Mac Basics: Launchpad is fast way to find & open your apps

http://support.apple.com/kb/HT5548

Some of the swipe and gestures features in your settings may also be part

of the problem you've experienced, since these can control the effects.

For reasons such as these, I prefer several older OS X technologies; and

some of those pre-X which were more exacting for single purposed use.

Good luck & happy computing! 🙂

There may be a setting in System Preferences> Exposé & Spaces> to change

how these windowed effects occur. {I have mine shut off, no need for them.}

Sometimes an application may be in hiding, and the icon in Dock will have a

Dot by it, showing it is open but out of sight. I try to use one window per app

and have them offset a little, so I can see/click-on the other one to bring it

forward or on top. Usually I have several windows, such as browsers, open.

A little easier with a larger screen, but all mine are smaller sized now.

So maybe the settings in Preferences may be somewhere to look?

Good luck & happy computing! 🙂