Keyboard combinations not working
I assume you mean the key combinations traditionally used to generate extended characters like bullets, umlats, and so on.  There are several places to check.

Check System Preferences : Language &amp; Text : Input Sources to make sure you are using the correct keyboard mapping (for example, "U.S."):



It can be very easy to switch your keyboard layout by accident, so you may want to be sure only one layout is checked.

If that does not help, look in System Preferences : Keyboard : Keyboard Shortcuts and see if there are any shortcuts assigned to the combinations you are trying to use: