If it's a CRT monitor (TFTs are the flat thin screens, CRTs are the bigger ones like TVs) then they have two wires running through them which will be visible, these are the aperture grill on the monitor and are normal, although they would likely have been there all the time.
_dobbo_ is spot on, my IBM monitor is the same way and if IIRC IBM and Dell both use Sony Trinitron picture tubes. There should be a line about 3.5" from the top and 3.5" from the bottom of the screen.
A bright horizontal line in the middle is usually due to something going faulty in the vertical (frame) scanning system. Difficult to say for certain without seeing it though.
Trinitron style damper wires are usually slightly darker rather than lighter.
