I have an acer aspire x3812, there seemed to be a problem with the power button so i replaced the case as trying to talk to Acer about it was long and painful. Once i changed everything over it booted once, shutdown put the case back together and now it wont boot at all.
alex i would first take the system down just to the ram and mb and see if it will post and give you a cmos beep code for missing the video card. if it wont power on take both side pannels off the new case and see if your missing a standoff and the mb is shorting out to the mb tray. somtime with cases and 3 party mb not all the standoff line up and you may need to use a rubber spacer to keep one edge of a mb from shorting out. new mb if there a dead short wont turn on. also check that mb and case shield cover for the back of the case is not shorting out. last thing to check is the cable connecting to the mb header. it easy to mix up the reset/power/hd cable and plug them into the wrong pins on the mb.
if you have a meter google power supply green wire test. see if the voltage are good on your ps. and that it turns on with no load on it. if you want the same mb there a service part# on the mb when it a vendor part you can google it or ebay it.