[jan-jaap]

NB: If you open the chassis of the 4D twin tower, you will learn about the "intrusion detection" switches. Basically, if you open the access panel of the main tower or remove the disk stack from the small tower and the system is powered up, the breaker switch will cut the power. Especially the main tower panel can be an annoyance, but it's not too hard to work around.

Finally: "This Old SGI" mentions that PSU problems can manifest themselves as disk problems! But if your disk doesn't function when attached to another system that's obviously not the problem.