dead imac? - Won't start past grey screen

If the Snow Leopard disc was an upgrade over Leopard, a drop-in

limited installer that shipped with some computers, it may not be

able to fully boot the computer for complete installation. If it is a

retail version, & not an upgrade drop-in, it'd be evidently marked.

• Troubleshooting Mac OS X installation from CD or DVD

Learn about troubleshooting Mac OS X installation from CD or DVD. ...

Learn about troubleshooting Mac OS X ... work with Mac OS X, you may need to install ...

support.apple.com/en-us/HT201817

If your computer shipped with Snow Leopard 10.6.x on grey-label

DVD media, to get a replacement from Apple (from AppleCare, etc

main online or by support phone) is a practical step. While an Apple

retail Store with Genius may be able to install Snow Leopard 10.6

it may not be the as-shipped kit with original software extras.

• Make an appointment at an Apple Retail Store Genius Bar
• Find an Apple Authorized Service Provider

U.S. iPod, Mac and iPad technical support:

(800) APL–CARE (800–275–2273)

Contact - How to Contact Us - Apple:

https://www.apple.com/contact/

You may be able to arrange an appointment with an official Apple store

genius for them to help check the computer. However if you get a new

replacement hard disk drive, and install it into the computer (or use a

cable adapter kit, to format a replacement before taking the Macintosh

apart; then once a new OS X is installed and tested in replacement HDD

the new drive could be swapped for the old one.) Once a new drive is

installed in the computer, the old one could be accessed by use of the

same 'universal USB drive adapter' such as OWC macsales shows on

site. A non-bootable drive that may have damages, can still be seen by

a computer to try & extract files off later.

•NewerTech Universal Drive Adapter USB: (incl. cables + power adapter)

https://eshop.macsales.com/item/NewerTech/U3NVSPATA/

examples of replacement internal hard drives & solid-state options:

https://eshop.macsales.com/shop/internal_storage/hard_drives_and_SSD

When replacing an old hard disk drive, you may consider to also replace

the cables; and be careful because the connectors can break. And more

details may be involved. See iFixit.com site for suitable Mac repair guide.

• iMac Intel Repair Guides - iFixit:

https://www.ifixit.com/Device/iMac_Intel

Note some build models of iMac require a similar Apple part number HDD
that has similar sensor inside, or a correct cable to use the right drive, so

the cooling fans don't run high speed; without the sensor being seen by

iMac hardware, fans will run. OWC offered an update kit with sensor to use

with those iMacs. You can also contact a reputable reseller to simply ask

questions, and note OWC macsales.com has several parts, & online guides;

you can find these by Mac model, https://eshop.macsales.com/upgrades/

Sorry to say that at this late (near 2AM local time) I'm unable to suggest a

simple method of talking your iMac into working. You may try the Opt key

(or X) instead of C key, so it can try to start from any startup disc or drive.

• What to Do when OS X install DVDs won't work:

https://duckduckgo.com/?q=what+to+do+when+OS+X+install+DVDs+won%27t+work&ia=web

• Shortcuts you can use while your Mac is starting up - Apple Support

• Mac keyboard shortcuts - Apple Support

A generalized list of handy startup options + shortcuts for Macs that run OS X:

https://www.engadget.com/2014/04/21/mac-101-a-handy-list-of-startup-options-for- macs-running-os-x/

https://www.engadget.com/2006/03/27/tuaw-tip-keyboard-shortcuts-during-mac-os-x- startup/

In any event...

Good luck & happy trails! 🙂

Start up in Recovery Mode, as per About macOS Recovery - Apple Support

1. Use the Disk Utility in Recovery to Repair the Macintosh HD.

2. Then try reinstall the OS X on the Macintosh HD while in Recovery.

If you can not repair or reinstall, then the Hard Drive is most likely dying or dead.

If OS X Recovery does not function, that may be due to it not having

been installed by an OS X version later than Snow Leopard 10.6.8.

There is a Disk Utility version on the Snow Leopard 10.6 install disc 1

and, if you still have the original system install-restore disc set, there

would be a 'hardware test' included. Read the label on install discs.

If you have the original install DVD media, that may be a way to see

if the computer's drive is OK; while there is a Hardware Test on those

they are not considered to be the final word. The drive may be bad

even is a test says it's not.

• Finding Hardware Faults: Explorting Apple Hardware Test & Apple Diagnostic:

https://computers.tutsplus.com/tutorials/finding-hardware-faults-exploring-aht-a pple-diagnostics--mac-60456

If you have an externally enclosed hard drive with a bootable system

backup clone, then you have a means to fully restore the Mac's HDD

to another replacement drive; or just run the Mac from the clone.

Some third party disc utilities are better than others for trying to repair

a failed startup; however it may be the original hard drive is bad.

Good luck in any event..! 🙂