There are several alternatives regardless of your Macintosh model. Try
these in the following order:
1) If you have System 7.0 or later, attempt to "force quit" the application
you were using. Hold down the Command (Apple), Option, and Escape keys. Your
Macintosh should present a dialog box which states: "Force <application name>
to quit? Unsaved changes will be lost." If you can move the mouse cursor,
click the "Force Quit" button.
2) If the "force quit" is successful, you should return to the Finder.
Restart your Macintosh from the Special menu. If the cursor is still frozen,
refer to 3) and 4) below.
3) If your Macintosh is still locked up, (screen frozen) check and see if your
Macintosh has a reset button. Most compact Macintosh models have a reset button
(also known as a programmer's switch on the left or right side of the computer.
Some modular Macintosh models have reset buttons on the front lower left hand
side. (Examples are: Macintosh IIcx, IIci.) Push the button marked "reset."
4) If your Macintosh is still locked up, (screen frozen) and your Macintosh
does not have a reset button, you can do a "warm restart." Hold down the
Command, Option, and Power On Key (button at the very top of the keyboard).
Your Macintosh should restart. This action is the equivalent of turning your
computer off and then back on.