it's called sticky keys.

To change StickyKeys options
StickyKeys is designed for people who have difficulty holding down two or more keys simultaneously. When a shortcut requires a key combination, such as CTRL+P, StickyKeys will enable you to press a modifier key (CTRL, ALT, or SHIFT), or the Windows logo key (), and have it remain active until another key is pressed.

Open Accessibility Options.
On the Keyboard tab, under StickyKeys, click Settings. Do one of the following:
To use the shortcut that allows you to turn StickyKeys on or off by by pressing the SHIFT key five times, select the Use shortcut check box.
To specify that when a modifier key (CTRL, ALT, or SHIFT), or the Windows logo key () is pressed twice in succession, the key will remain active until the key is pressed again, under Options, select the Press modifier key twice to lock check box.
To turn off StickyKeys when a modifier key (CTRL, ALT, or SHIFT), or the Windows logo key () and another key are pressed simultaneously, under Options, select the Turn StickyKeys off if two keys are pressed at once check box.
To play a tone to indicate when a modifier key (CTRL, ALT, or SHIFT), or the Windows logo key () is pressed, locked, or released, under Notification, select the Make sounds when modifier key is pressed check box.
To display an icon for StickyKeys on the taskbar when StickyKeys is turned on, under Notification, select the Show StickyKeys status on screen check box.

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