Keyboard & mouse don't wake the computer

I have both the keyboard and mouse set to wake the computer, but it doesn't work.  I am using an external monitor on my laptop and press the sleep button.  But am unable to get the computer out of sleep by using the keyboard or mouse.  I checked the BIOS and all is set correctly there too.   Does anybody know how to fix this?  I have another computer sharing the external monitor and that one comes out of sleep using the keyboard and mouse; all settings are the same.  I am using Windows 7 Home Premium and it's a laptop.