|"Third, apparently some screws to fix the keyboard (on the upper part) are missing. Is this situation might lead to the keyboard stop responding?"|
When you boot from the Linux CD, it should be obvious whether the keyboard works or not when you do certain things that require typing.
Ask the owner why the screws are missing, and if he (or she) or someone has been fiddling with keyboard wiring or wiring connector.
If it has a single PS/2 port, that should work with both of either a PS/2 keyboard or a PS/2 mouse, or it can be used with both if you use a standard Y cable - PS/2 male to 2 PS/2 female - meant for connecting both.If the PS/2 female connectors on the Y cable are colored, green is for a mouse, purple is for a keyboard, or if they not different colors, which thing they are for may be molded onto the surface of the female connectors.
A USB keyboard requires that the bios Setup has the USB controller enabled, it is by default, and that a setting is enabled USB Legacy Devices or USB Keyboard, or similar, in order for you to be able to get into the bios Setup - in newer bioses that's usually enabled by default - in older bioses that's usually NOT enabled by default - but it should work while booting and in Windows otherwise.