IMac Model No: A1312 running OS X fails to boot.

Question

I work in a school. We have a number of Mac devices. One being an iMac Model No: A1312 running OS X. Today this machine failed to boot – instead it started up but after about a minute of a screen with the Apple and the spinney cog wheel it dumped to a dark grey screen with an active cursor and responsive keys on the keyboard (the beep was heard when pressing the spacebar for example) but no log on box or other screen activity.
I have tried all sorts of diagnostics – hard drives comes up as ok. Reload of OS X – twice but always the same result.
Any suggestions as to what’s wrong please fellow Forum members?

Answer 1

Thanks for your lone response @rkaufmann87 I'd have thought more responses were offered - perhaps an indication that this is a rare issue.
There are no peripheral devices connected - the KB and mouse are wireless and clearly communicating with the device well. I've tried the suggested resolutions without the LAN cable connected and as stated in my OP with the LAN connected (from two different locations) can access the support pages etc. and indeed the machine has spent in excess of 4 hours powered up and twice reinstalling the OS X.  All seems to go well but then after the restart up comes the standard start screen with the Apple Icon and the spinning cog wheel then after a minute or so it dumps out to a darker screen with just the mouse cursor visible. The mouse moves the cursor and pressing various keys on the KB brings beep responses.
As a School Network Manager, working with a very tight school budget, I'd rather get the machine sorted with Forum help and my in house effort if at all possible.  The last iMac job I put out to a recommended Apple repair Workshop was for a replacement screen to a still under warranty new 21 inch iMac and that cost about half the value of the machine to get done - ouch!