1.Make sure that your iPhone cable works and try using another cable that fits your phone.
2.Check for any updates in iTunes. To do this open iTunes, click on the box up in the corner of the iTunes windows and select "Show Toolbar", now since you added the toolbar to iTunes, then find file click and finally select "Check for Update"
3.If these still did't work try deleting iTunes and retry downloading iTunes from: http://www.apple.com/itunes/download/ and roll down and select download.
This should clear your problem