I have music on my iphone, but Itunes says 'Music - zero items' when iphone connected. How do i manage my songs?

Background info: I have music on my iphone that i would like to change / delete / update manually. Software versions of both itunes and iphone are up to date.

So, in chronological order:

When i connect my iphone to my PC, itunes detects it. Fine. No problem.

I click on the 'on this iphone' tab (where I would expect to see the music i know to have on my iphone)... It says 'Music - zero items'. Hmmmm - i know i have over 1 GB of music on there...

I click on the summary tab for my iphone. 'Manually manage music and videos' is checked. The status bar at the bottom shows i have over 1 GB of 'other' information on my iphone, but no music.

Basically what i'm after is being able to delete and add music from my itunes to my iphone as i see fit. At present i am unable due to the reasons outlined above. Tried contacting Apple direct but providing me with only 140 characters to describe the problem to them is.. well... pretty w@nk.

Any help appreciated- have been scouring the discussion boards but cannot find anything that correlates directly.

Thanks in advance