iMac not booting!!

My 2011 iMac has not been working for at least 2 years now, recently i dragged it out and plugged it in and it seems to start up and show the apple logo as if its about to start normally, although it will always change to a fully white screen and remain that way unless i restart it by holding the power button or unplug it from the wall.

I have tried every way to reboot my iMac like using safemode, internet recovery, etc. Despite trying endlessly it will always go onto a white screen and not boot up properly. PLEASE somebody help me out?!!