Use these key combinations in the Project Explorer:

Press To
ENTER Open the selected file from the list, or expand and collapse the list to show its subentries.
SHIFT+ENTER Open the Code window for the selected file.
F7 Open the Code window for the selected file.
SHIFT+F10 View shortcut menu.
HOME Select the first file in the list.
END Select the last file in the list.
RIGHT ARROW Expands a list and then selects a subentry in the list each time you press it.
LEFT ARROW Selects a subentry in the list and then moves up the list each time you press it until the subentry list collapses into a folder.
UP ARROW Moves up the list one entry at a time.
DOWN ARROW Moves down the list one entry at a time.