IDE Hdd problem

I am trying to repair a friends pc which stopped booting (wont even go through post) I disconnected the hdd and post screen appeared and detected the cd rom ok, I then tried a spare hdd and the same problem persisted, tried the original hdd in a spare pc and it worked fine, I have tried changing the cables but to no avail when any hdd is connected the pc powers up but just sits there with a blank screen