Making Photoshop, PhotoShop Elements, and other programs work.
I have noticed from time to time that for some students Photoshop in the classroom does not seem to be working. When this happens check the following.
1. Look at the menu bar, if most of the menu items are ghosted a process is not finished. Either, Press the return or enter key to apply the change.
Or, press the escape key (Top Left on the keyboard) to terminate and cancel the process.
Look at the options bar... to complete or apply the process click the check mark, or cancel the process by clicking the Universal "No" sign.
2. Look at the layers palette. You may be working on a type layer, or an adjustment layer, or an empty layer, not the one you want.
Make sure the proper layer is activated by clicking on the layer in the layers palette with the mouse. (The selected layer will turn Blue). Check to see if the layer you are working on is locked.
To check for a "hidden" layer press control (H) on the PC or on the Apple Command (H) to activate the hidden layer.
Check the tool settings in the options bar, a value may be set real low or at zero.
Check the dialog box to see if "preview" is turned on.
Read Ben Wilmore's articles at digitalmastery.com for more ideas and insights. Or, do an internet search for the solution.
Still can't make it work? As an absolutely last resort (You have tried everything) re-install the program.