Peter, the only thing I can suggest you to try is hit Reset To Defaults on Tools > Customize
But before you this, keep a copy of your current settings using copy setting wizard (found on the start menu under SolidWorks tools OR with no document open, go to Tools > Save/Restore settings).
Deepak is on the right track. We believe this is a problem with your UI customization which is stored in the registry. Take a look at the following forum posts....
In SolidWorks 2013 we have added a fix that we believe avoids the bad display if the registry states get out of sync. If a bad CommandMgr state is detected, it cleans it up when SolidWorks starts up.
Thank you very much for you help. Reset to defaults didnt help. I reinstalled SW and now it is working properly. Problem solved!