[tw]

The simple ones mostly traced back to DOS:
Alt-F4 - closes a program; important when mouse fails, screen goes funny, or system has become funky. Standard everywhere; even back to Dosshell.

Control C - copy; also known as Control Insert on older Windows and Dosshell.
Control X - cut
Control V - paste; also known as Shift Insert on older Windows and Dosshell.
F3 to repeat last keyboard entry on MS-DOS or Command Window (text) screens.
F1 - Help
Alt Tab - select things when mouse cannot.
Tab - may also be useful on some screens when nothing else appears to work.

Control P - activates printing; avoid (if system is not fully functional) since it can sometimes hang programs or delay computer response.

When Windows goes funky and funtions in Start are needed, then try combinations of 'Control or Alt' 'Return or Esc'.

On powerup, F1, F2, F10, or Delete may provide BIOS options (also comprehensive hardware diagnostics if computer manufacturer was a more responsible type).

After powerup and when Windows first starts to load, Windows loading can be modified by F5 or F8.

A minimal and yet tech useful subset of keyboard shortcuts.