Unsealed court documents reveal that most Dell Optiplex desktop workstations sold between 2003 and 2005 have one unique feature:
Electrical capacitors that crack, pop and leak:
In Suit Over Faulty Computers, Window to Dell?s Fall - NYTimes.com
Not only were the faulty capacitors extensive, but Dell was so overwhelmed by the problem that it launched a cover-up initiative to keep customers confused as to what the root problem actually was, but failed to recall the affected models (most of the Optiplex line).
I still have one of the computers in question and knew of the mobo problems 2 years ago. Since I cannot trust running anything serious on it, I have it running old software I use to backtest stuff, and I never switch the machine off, ever (powering on a computer is the point when the motherboard components experience the most EM stress). I didn't know it was the capacitors, but I knew something was up when the mobo on that machine was replaced twice when it was my main PC workstation at the office.