I had this once, a long time ago after a direct hit of lightning to our house. In my case the overload actually seemed to have come in two ways, once over the telephone line (yes, a modem. It was that long ago). And secondly over the PSU (as an aside, the PC was actually unplugged at the time - but the electricity jumped from the socket to the cable lying below! - I saw the flash under the desk from my sofa at the time). Anyway, both the PSU and the modem were fried, but the rest was OK, IIRC.