Intel graph card does not display thru displayport

[pamplemousse]

hi all,
i am very new to the linux world. here is a brief introduction to me and my set-up.
i live in sw france. i got a company desktop computer which was about to be withdrawn by out IT - renewing the computers. i want to connect it to my tv to use my tv as a screen but something does not work. the computer is a HP compaq model, i can't exactly tell which one. i installed linux mint (first time ever). here is the basic info:
os is linux mint cinnamon 64-bit
cinnamon 2.2.13
linux core 3.13.0-24 generic
CPU is intel core 2 duo E8400 @ 3.00GHz * 2
graph card is an intel corporation 4 series chipset integrated graphics controller
i cannot see any driver or peripherics (not sure of the english translation on this one) when i am trying to show them through the administration panel

so my issue is: the graph card has VGA, displayport and another VGA male connector (with pins) outputs. i want to connect the display port to my sony bravia tv and have bought a displayport to hdmi cable. the computer recognises the TV as a 2nd screen but the TV does not see any input. i am assuming the graph card has an issue with displaying thru displayport. i have tried either to consider TV as 1st screen but also to simply disconnect the VGA cable but still no display.
any help is welcome
cheers