Alby_da_Wolf on 18 September 2014
Have you checked all the connectors?
Also, if Windows 7 was directly put in the new PC already installed on the HDD, did it perchance previously run on a system with 2 HDDs? In that case check whether some important files and directories weren't in default positions but customised (for example, I always put the swap file in a dedicated partition, to prevent it from drastically increase fragmentation of OS, programs and data partitions): if some of them were on a different HDD, and the new system just uses one of them, it could cause errors (although in this case, if the OS can start at all, it should show you an error message when the failure happens).
