Using the power-save (or standby) mode instead of keeping your computer running constantly can save quite a bit of energy, and you will be able to resume your work session at any time. There are several simple ways to get a Dell desktop computer out of power-save mode.
Move the mouse in a circular motion. Most computers are set to immediately resume once the mouse is moved.
Press any key on your keyboard. Most computers are also set to resume once a key is pressed.
Press the power button on your computer. Don't use this method unless neither of the above options works, as some computers are set to turn completely off when the power button is pressed. However, if neither the mouse nor keyboard gets your computer out of power-save mode, this should work.