Hi, lately my iMac hasn't been waking up from the usual mouse click, have to press the power button for the screen to come on. Now it's not coming on at all. Have reset SMC and NVRAM. Unplugged, restarted etc. Start up noise plays, fans run etc but get nothing but a black screen. Lights on the Magic Mouse and keyboard also don't stay green for more than a couple of seconds either (have changed batteries in both). Please help, need this fixed ASAP!