Can't start up

Will attempt erase & reinstall tomorrow or next day. Putting it off because unsure if I can get everything up and running as before. Many thanks for your diagnostic test and support. Used disk utility to make a disk image in addition to other backups. Never used that feature before but assume that is what you meant by backing up with the disk utility.

I end up buying software packages with all kinds of cool but unnecessary utilities which years later lead to conflict problems when Apple updates. I'll have to learn a new way of working leaner with only what I need and use regularly. Many thanks for the lesson in safe computer use.

Clean install doesn't seem to work on late 2009 iMac. Tried twice to reinstall Yosemite from boot drive after wiping disc but no luck. Any suggestions on how to reinstall OS 10.10.3 from Apple. Writing from iPad No access to iMac.

Yes, printed out and followed Apple support instruction for erase and reinstall of OSX Yosemite. Did the same with all your instructions but never got to the where I select only users in set up assistant.

Restarted Mac holding down command R, selected utility disk and continue. Selected iMac internal HD volume, chose extended journaled format and clicked erase. After erase quit disk utility and selected reinstall OSX and continue. Install appears to be going fine Apple mark and bar appear but the process including automatic restarts) never occurs/ finishes. Left computer on overnight but woke up to a gray screen with no Apple mark or anything. I have original 10.6.2 iMac OS X install DVD but not sure what to do.

Apr 28 21:54:34 localhost opendirectoryd[123]: 125.1 - ODNodeCreateWithNameAndOptions failed with error 'Unknown node name' (2000)

Apr 28 21:54:53 localhost configd[113]: InterfaceNamer: No current set

Apr 28 21:54:54 localhost configd[113]: [bootp_transmit.c:213] bootp_transmit(): bpf_write(en1) failed: Network is down (50)

Apr 28 21:54:54 localhost configd[113]: DHCP en1: INIT transmit failed

Apr 28 21:55:13 iMac.local Unknown[388]: Setting boot completed.

Apr 28 21:55:24 iMac.local Unknown[388]: Keyboard Layouts: duplicate keyboard layout identifier -16899.

Apr 28 21:55:24 iMac.local Unknown[388]: Keyboard Layouts: keyboard layout identifier -16899 has been replaced with -28673.

Apr 28 21:55:24 iMac.local Unknown[388]: Keyboard Layouts: duplicate keyboard layout identifier -16900.

Apr 28 21:55:24 iMac.local Unknown[388]: Keyboard Layouts: keyboard layout identifier -16900 has been replaced with -28674.

Apr 28 21:55:27 iMac.local OSIESpringboard[402]: Can not connect to /var/run/systemkeychaincheck.socket: No such file or directory

Apr 28 21:55:27 iMac.local OSIESpringboard[402]: Failed to unlock login keychain.

HELP

Connected to internet with category 6 ethernet cable directly from iMac into router. High speed internet (optical fiber connection). Safari in recovery mode, WiFi on iPad and iPhone, and internet on wife's computer all good, so don't think it's a network issue. Ran permission and disk repair in Disk Utility and says disk fine.

Since this is first time for me to try clean install, and this computer came with Snow Leopard DVD (10.6.2) install disk (before Apple switched to downloading OS), I'm guessing the normal method of just clicking reinstall after erasing doesn't work the same as on later-built machines. Have you hear heard anything like this?

Tried erase and reinstall again but second time process started and usual messages appeared (as with first time) but took a really long time (over night) and ended with light gray screen with no Apple mark or way to access computer.

Tried to put in install DVD to see if iMac would boot. Looked promising for 1/5 of start up bar but then screen turmed gray again. Then had big problem ejecting DVD. Finally got it out.

Tried to boot from auxillary external HD holding down option key but no luck there either.

Now can only access recovery disk but nothing else.

😟

As you suspected looks like hardware fault. Called Apple and they said probably graphics controller or logic board.

If it didn't happen during this attempt at clean install, it would have happened during regular usage.

Many any thanks for your kind support. Will have to discover life without a computer for a week.

In Japan, if Apple still has parts, they will repair your Mac. They charge a flat rate of $420 but change and repair everything they find defective. Smaller repair shops might do it for less, but Apple is more reliable and does an excellent job.

I like my 2009 27 inch iMac which has an internal DVD and 16 MBs of RAM. The newer ones have better graphics but I figured a fix should last me a year or two so I don't need to shell out for a new one just yet.

I should have realized it was an internal hardware issue and not an extensions conflict when my external clone started up with same problem. Erased the clone and backed up user folder and other folders manually. First time not to have a working clone to startup from and one of the rare times computer actually broke down.

I've used Macs since about 1984 and mostly managed to remove problem extensions when conflicts occur. From now on I plan to keep my system as simple as possible. I am fond of cool utilities and repair programs, but will have to keep them to a minimum. They come in bundles so I end up installing utilities I seldom use.

Thank goodness no pressing work to finish while machine getting repaired.

Thanks again for your help and advice. The Apple support community is really lucky to have an expert like you!