I've just rebuilt my pc inside a new case and it's now running incredibly slow and everything stops responding and freezes every few seconds, I've no idea what's wrong, any help would be great thanks.
I would take everything apart and redo it all. Do you have a big air cooler on your cpu? Moving your Motherboard from one case to the other may have flexed the board and moved the cpu under the cooler, could have moved the ram. Check all the cables to make sure they are seated correctly.