If four internal drives all died basically at the same time, then the only possible conclusion to draw is that either the cable connecting all those drive bays together has gone bad, or there's an issue with the SATA controller on the logic board. The only way you're going to know for sure is to find someone who can swap one of those parts out. Cross your fingers that it's just the cable, because if it's the logic board, you will be paying dearly to get it repaired. You may also want to hurry. Apple only stocks parts for units up to about 5 years old, so all the 2007 lines are next on the chopping block.