Sounds like you have an intermittent connection issue with either the SATA power or data cable. This may be because of a dodgy cable or the connection on the motherboard. If you keep the replacement cables you now have and try the 3.5" disk and it works also, then dispose of the old cables in a recycling facility. If the 2'5" disk has further intermittent problems, then the issue may be with the motherboard and you should flag the problem to W-O-S directly. @birdman is right in that the box should recognise any standard SATA disk, whether formatted or not and then give you the option to format/initialise it.