This is being posted from a laptop, as the desktop in question is unusable at the moment..
I recently transported my desktop in the back of a car for a 10 hour drive to UC San Diego. When I set up my computer in my dorm, it turned on fine after I hooked everything up. I turned it off and later when I tried to turn it back on, I heard this one long beep 3 short beep error code from my motherboard. I looked up the error on google and found that it means its a problem with the "Video (EGA) Display Circuitry".
I was unable to get any display and every time I turned on my computer I received this error code. Today, I borrowed a screwdriver and opened it up to see if anything had unplugged itself but everything looked generally fine. Before I opened it up, I made sure to flip the power switch on the back of the machine to make sure everything was fully off. I made no changes to the internal hardware, but after I replugged in my desktop and flipped the power in the back on again, the computer turned on with two short beeps, several seconds apart from each other, but the display worked!
I was excited and replugged in all of my mouse and keyboard and such, but to double check that everything was working, i restarted, and that's when i got the same original error beep code.
What is wrong with my perfect until now machine? I bought it in January and it's fairly high end FYI.
If you know how, I would remove the RAM DIMM(s) and re-seat them and also the Video card as a 10 hour road trip may have unsettled them in their sockets so you get an intermittent electrical connection.