In short: there are a few servers in a small server room. Being cheap general not-really-business-oriented machines, they did not necessarily have good safety features from the beginning, and what's more, they could be arbitrarily modified before being brought to the room and installed there. How could such a server die a sudden and dramatic death, with the perpetrator able to make practically any preparations for the sabotage?
I've heard some kinds of chips can explode somehow, but if this scene sounds absolutely implausible, consider what could be different if the servers were manufactured a decade or two into the future.
As much as I'd like to learn if blowing up a computer is in any way possible, I also have two conditions specific to my story:
there must be no visible clue of intentional sabotage — it must look like a technical problem upon visual inspection (so, no explosives inside the server case)
the attacker must be able to remotely* start the process at short notice, with at most 3-4 days from the start signal to the final catastrophic event
* Meaning: from outside the room. E.g., hacking the system, changing voltage or air conditioning of the room. No inside traitor, however.
I'm writing a story involving an Internet-connected server which at some point explodes. The system is optimized for the compilation and execution of simple programs as well as for various computations, working as a cloud testing environment for a local community of computer scientists. (The reason why anyone would want to make it blow up is, frankly, difficult to explain.)
The tiny server room where it is located can be assumed to be reasonably safe (physically), however security practices are not the priority for the inexperienced sysadmin. Therefore, the chance of initial compromisation is very realistic (i.e., the outside person installing the server may loosen some screws or even infect the system, and the sysadmin would never notice). Also, the never-updated system could be hacked at any time, since the server is connected to the Internet.
Whether it was from personal experience or science fiction films, I thought the processor overheating would do the job. For example, a bug in the system could suddenly cause a massive amount of computations to be performed, generating constant intense load on the processor, which would ultimately cause it to overheat (and explode...?) However, it now seems to me that more problems need to arise to lead to such an extreme outcome. Since nobody around the server room really knows or cares what is going on (as long as the server is up), and the computer scientists never visit the room themselves, the attacker has lots of opportunities.
If an explosion is really improbable, a similar dramatic incident could happen instead, e.g. the spinning fans could slip off or the box could fall to the floor or catch fire, leading to disastrous consequences and possibly destroying nearby objects in the process (which, come to think of it, could be the ones exploding subsequently). As I noted, the person setting up the server is free to prepare it for anything.