PS3 - sound but no graphics/video

I have been given a PS3 to look at and see if I can solve the problem of it having sound but no graphics or video. To try and eliminate the HDD I have tried to use two HDD's and there is no difference. Any ideas?

The hard drive(s) should make no difference to video, and by the fact sound is coming out suggests the drives and system are working fine, the no video on the other hand is a toss of a coin, to me it can only be one of two things, hopefully it's a simple cable issue, try using different cables, or if it has a secondary connection type try that, if this reveals results you have your answer, well you know where to look more closely at least as it narrows down the possibles. Now the worst case, it could be the units graphic display has gone, only way to figure\confirm this is to take it to a repair place, unfortunately I have never touched one of these, so not sure on how it's built, if it has it's own graphics card it may not be as bad as can be feared, but if it's onboard video then it may need a new board, I can only guess at these possibles as I have not dealt with one before, but these are the logical conclusions I can think of, others who know it more than I may know of such issues, but hope this gets you started if nothing else.