SNDS, "Sudden Northwood Death Syndrome," refers to the vulnerability of Intel's Pentium 4's "Northwood" class processors to overclocking. Overclockers soon realized that after 1.7 volts, the processor would become gradually unstable, and eventually be completely unusable. The rate at which this happens varies entirely from processor to processor. That is, to say, it could take days, or even months, but it always happens, and always occurs at 1.7 volts (or higher, which obviously accelerates SNDS). Once a processor has contracted SNDS, the prognosis is very grim. Even if you return the core (CPU) to stock speeds, the damage is already done, and could even still progress at stock voltage. Overclocking is a great way to improve hardware, but it can be dangerous and has its risks... only attempt to do so if you have a strong background in computer science.
Guy 1: I overclocked my Northwood core from 2.6 to 3.6 GHz, but I had to increase the voltage for stability.
Guy 2: How did that work out for you?
Guy 1: Everything was fine and dandy until the computer hard-locked.
Guy 2: Sounds like SNDS...