Kinda obvious, but have you checked if all your HDD connectors are securely fixed ? SATA connectors have a very annoying habit of coming loose at the slightest touch and that will give you all sorts of HDD problems. And if they're too old, maybe try replacing them. Check the power connectors too while you're at it.

Normally an HDD will never ever say 'drive not ready' unless something is seriously fricked up.