insomniachollie wrote:
Have you also considered that maybe they worked out that you tried to replace it yourself and in doing so voided the warranty? In which case packing it back up and sending it back to you as it was would be the entirely correct thing for them to do.

Which would also make it a very expensive and futile thing to attempt to sue them.
Exactly. Never try to repair a computer yourself unless you know EXACTLY what you are doing, for just this reason, unless they have given you explicit instructions to do so. You've likely voided your warranty, which would explain why they just put the old one back on and sent it back to you. That means you're going to either have to pay them to repair it or buy a new one.