Turns into blocks while posing, or permanently? If it's just while posing then somehow Manipulation draw styler has been turned on - Edit>Preferences>Interface and select None for the option for most tools, Active Pose has its own setting which is available from the Tool palette when the tool is selected (View>Tabs>Tool).

If it's always like that, and only when you start posing (that is if the figure loads looking normal) then check to see if there are updated drivers for your video card, if there are see if using those helps.