If you are worried about what happens on your PC in your absence, and you want to monitor and spy on all those that use it, you need a program like Total Spy.
With Total Spy you can store everything that has been written, consult the webpages visited, applications run, changes made to the clipboard, make screenshots of everything happening (that can be used as proof), emails sent, etc.
The whole process is invisible to the user, who will never know they are being spied on. Only you, with a predetermined (by you) key combination have access to the program and can consult the information it has stored.