Lost command keys

Please read this through and please reply to the actual problem, not just the
first 4 words:
When I'm using ANY Windows application or programme, when I type Ctrl+S,
Ctr+B, Ctr+F, Ctr+P nothing happens. They used to work but not any more.
Other similar command still do (like Ctr+V, Ctr+C, Ctr+X, Ctr+Z, Ctr+W,
Ctr+I, Ctr+U and Ctr+V).
Any idea on how to fix this?