Coloured green & red lines on screen

Try using a different monitor. Borrow a friend's monitor and use that. If the lines go away, this means your monitor is bad. Buy a new one.

If the lines also appear on the other monitor, then the problem is inside your PC. Probably your video card has gone bad. Buy a new one.

Might also be bad video ram. It may start appearing as the ram modules start to heat up.

Also what kind of connection are you using? if your using a blue VGA cable - if it's loose it will tend to distort the image thanks to it's analog nature.