How can I see all keypresses on the keyboard?

You could use AutoHotkey and KeyboardHook to see what keys are being pressed. You only need to create a script with this line

#InstallKeybdHook

Save the file with and "ahk" extension and run it. Then in the Systray do a right click in the proper icon and select open. In the menu select View->History.....press F5 to update. This two sites could be of some help:

http://www.autohotkey.com/docs/commands/_InstallKeybdHook.htm

http://www.autohotkey.com/docs/commands/KeyHistory.htm

What you need is a Keylogger. For example, you can use Actual Keylogger, a free keylogger which runs hidden in the background and automatically records all keystrokes.

Alternatively, you can use PassMark Keyboard Test. It's a shareware with a fully functional and free 30 day evaluation. It allows you to quickly check that all the keys on your computer keyboard are functioning correctly, check the keyboard LED's and look at the internal scan codes being generated by the keyboard.

A really quick Google search turned up this: http://keyboard-tester.software.informer.com