How can you select text in a windows command prompt without using the mouse?

As Ignacio said however you need to ensure "QuickEdit Mode" is enabled from the CMD properties.

1. ALT+Space -> E -> M (now in mark mode)

2. move the pointer using arrow keys

3. Hold shift and select the area to copy

4. Hit Enter and it's now on the clipboard

AltSpace, Mark, arrow keys, hold Shift, arrow keys, Enter.

Please be aware, that ALT+Space > E > M only works on English locales of Windows. In other language versions the letters after the ALT+Space can differ. e.g. on a German version of Windows have to press ALT+SPACE > B > M