Speed or SPD? If you mean the latter, CPU-Z requires the SPD module on the memory DIMMs to provide that information and if it's not in a format recognised, then it'll be blank. Another possible issue is that CPU-Z needs to be run in Admin mode: right-click on the icon and select 'Run as administrator' as this can sometimes help with that problem.
Still like to get it to work now that I've decided to upgrade memory, don't want to have to disassemble the pc to find out what memory is installed. Is there any way I can find out the present memory configuration without having to take off the panel.