Press Ctrl-space to activate. Sometimes a message will say 'No completions found' or something like that in the completion frame, and sometimes in the message center near the bottom of the window. Usually, if you press Ctrl-space after a dot ('.') in chaining, you will come up with a list of possibilities to choose from. If you are not on a Windows system, it may be different.

The problem is, if you have a non-English system( mine is Chinese), Ctrl + space is the hot key for changing input method between Chinese and English. And as far as I know, there is no way to change the hot key.That means I can't use auto complete now.