mid-2011 20.5" iMac has no power following RAM upgrade
Unplugged iMac, removed 2g memory modules, replaced with 4g, no response from power button - reconfigured to old memory modules and still no power on -
Tried resetting PMU several times - attached external USB hard drive and no power light on drive so no power is coming through the USB port.
Any idea what to do next ??
iMac 21.5″, macOS 10.12