It could be the cable has been damaged and a pin has bent or a wire inside the cable has fractured but if you are sure the cable is not at fault then you could try the following.
I have had this a few times and generally one of two things tends to fix it but both involve unscrewing the machine:
1. removing the internal power unit and cleaning the connection pins
I am not sure why but sometimes dirt grime or light surface corrosion seems to stop the machine receiving the correct power and I lose the picture. (please be careful doing this as it is obviously a mains power supply so don't do this if you are not confident!)
2. This is more of a long shot but the GDROM drive may have jiggled loose especially if it has been in transit and does not have screws holding it down.
I tend to have the black screen problem on my machine with a GDEMU board as it is not as secure as the GDROM drives and if I reseat the GDEMU board it can also fix the picture.
These are just my experiences and maybe someone else might have an idea but thats what i usually do.
Hope you solve it