To all of those out there with an Acer Aspire L100 SFF that has decided it will no longer boot -
Symptoms: fans spin up, DVD spins up, possibly HD spinning up - no power, HD or network lights on front panel.
Previous Fixes: Changing out 3 capacitors on the mainboard, re-seating memory and processor
I tried all three of the fixes above and still no joy. I discovered to my surprise that this PC, due to it's heat "issues", had developed a malfunction similar to the XBOX 360 and Ibook G3...it's video chip had developed some connection issues with the mainboard. Due to the heat, the BGA solder connections under the chip has either flexed and become disconnected or corroded with the same result;
Try this: Remove the DVD/HD "sled" - Using 3 fingers, put pressure (not enough to break the mainboard, but a fair amount) on the heatsink for the video chipset. While doing this, press the power button. If it powers up, this is your problem. You might have to try a couple of times with varying amounts of pressure on the heatsink.
Tools: Needle nose pliers,philips screwdriver, small flat blade screwdriver, new heatsink compound (I suggest AS5), a heat gun
The fix: Firstly, the mainboard must be removed from the case, and the heatsink removed from the video chipset. To remove the push-pins, use a pair of needlenose pliers from the back of the mainboard to squeeze the expanders to release the pins. If yours is like mine, after removing the heatsink, you will find that the thermal compound has hardened and is no longer effective...have some AS5 handy.
Second, place the mainboard on a flat work surface. Make sure memory, cables and mini-pci wireless card have been removed. Starting about 4 inches above the video chip, put your heat gun on low setting and ove a period of about a minute, move slowly down until you are about an inch above the video chip (this is to heat it slowly and not cause damage) hold there for 30 seconds - you should notice the solder on all the connections around the chip change sheen from dull to shiny - over about 30 seconds to a minute, slowly lift the heat gun away - letting the heat dissipate slowly. Turn the heat gun off and let the board cool for 10-15 minutes.
Third, put a thin layer of AS5 on the video chip core and reapply the heatsink, being careful not to chip the core. then proceed to reassemble the machine.
I did this repair myself 2 days ago...still working great!