1st thing I notice is that you have selected a scatter chart subtype as markers without lines. If you want lines, I would probably select the chart subtype as markers with lines.

2nd thing I notice is the "gaps" in your data. You may need to change the "hidden and empty cells" setting, so that it will show lines across these "gaps". http://excelribbon.tips.net/T006289_...pty_Cells.html