You have an International keyboard layout set for your keyboard (probably United States-International keyboard layout - but there are others).
With this keyboard layout the ` keystroke becomes a modifier to enable entering of special characters.
To get a single ` character you will need to type `+Space.
Alternatively change the keyboard layout to the appropriate non-international version.
See Add a keyboard layout for more information.
Type International and Special Characters using the right Alt key or the following modifier keys: Apostrophe('), Accent Grave(`), Quotation Mark("), Tilde(~), and Circumflex(^). To type just the modifier key by itself, type Space following the modifier key.
Source Help with Microsoft Keyboards US-International | School of Languages, Cultures, and Race | Washington State University