Black Screen At Startup, Chimes OK, External screen OK

Hello. I replaced the power supply and hard drive to iMac recently. After the fix, the iMac boots to a black screen. I can here the chimes and if I hook up an external monitor, the screen shows on it. I reset PRAM. I don't see a faint image on the iMac, however. Any troubleshooting steps anyone can recommend or maybe you know the issue? Thanks in advance.

Tony

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Could it be a bad of loose LCD cable? Thanks.

Tony

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Tony makes a great point. Recently watched a video where someone purchased a bunch of iMacs and they had display cables that where not plugged in. I don't have any familiarity with the iMacs however, sometimes if cables are hard to connect, you might think you got them and then they shift when you move a component. It's also possible you fried the backlight on the LCD.

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