pixelated green / grey apple logo on boot

Hi All hope you can help , a friend of mine has a g5 and whats happening is when powered on I get chimes , then the apple logo and cog , the problem being the logo is not grey its got green wavey lines through it , the wheel spins with pixelated green dots , the does not boot but goes to a white screen , then nothing , I think it's maybe the video card ( if there is one installed ) , if not then im stumped , I am an I.T Tech but mainly Windows , Desktop's e.t.c so do not hesitate to use I.T language replying !

Thank you for your responses in advance.

Shaun.

P.S HELP !!!!!!!! lol