Why won't my iMac boot to any device?

Why won't my iMac boot to any device? I’m trying to fix my iMac. It will not boot to any kind of device or partition. It will startup and chime, and it will show the progress bar, which will then freeze about halfway through indefinitely.
Asked by: Guest \| Views: 188

Total answers/comments: 1

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bert [Entry]

"I think you’ve given me enough clues to identify the problem.

Sadly, your dedicated GPU board has failed. The clues that tell me:

Intel graphics engine is working (Target Disk Mode) you see the Icon on the screenYou see odd symbols and other artifacts when booting up off the disk

Here’s the replacement part you’ll need: ATI Radeon HD 2600 Pro w/256 MB - Apple P/N 661-4426

You should also get thermal paste and thermal pads to remount GPU board to the heat sink.

Here’s one source: ATi Radeon HD 2600 Pro 256 MB"