How to fix a screen cable problem on a MAC desktop?

[Daisy]

So I have had my mac desktop since 2007 and can barely afford to fix it or by a new one. I am not sure what model it is, but it looks like this: http://img.tomshardware.com/us/2007/09/0...ops_06.jpg

Not to long ago, it started getting multi-coloured lines vertically down the screen. Then out of no where, a huge black bar came and cut off part of my screen to the right of my computer. Now it repeats the screen before it. So today I went on Safari and the duplicated part on the right of the black bar started flickering. Also some parts of my screen are lighter than others. I have done some research and they say it is my screen cable that has come loose.

Please help!
Can someone please give a step by step?