Why isn't my photo shop pen working?

[linden sprunt]

Hi All I have used the photoshop pen frequently but for some reason cant get it to work today, dont seem to be doing anything different, colour is set to black on a white background, brush setting is 6px, pen set to path. When I joint the dots to creat a path, then click to stroke, it isn't bringing up the brush (or any option)to stroke the line?? HELP Linden

 

[Berbatov]

Did you create a new layer? Whenever you are on a layer with a shape, for instead, you can't stroke a path

 

[linden sprunt]

Thanks for reply. I have opened a new page, imported an image, created another blank layer and made it opaque so I can see the one below and I am using the pen to go aroung the images below. It's just happened again, started using pen, first two points worked then I checked my brush with and incrreased it from 5 to 6 px and then the pen stopped working again?