[TTT3]

Imac boots normally, everything works and after a few minutes the screen starts to collaps from the sides and eventually completely black and then reboots.

I've tried resetting pram but nothing.

Is it a hardware problem or something else ?

Can someone help me please ,

thx

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Imac is 4 years old

[storer]

so it is an iMac CRT/G3 or a G4?

[TTT3]

G3

[Eriamjh]

Do you get a vertical line down the middle? If so, the horizontal sweep circuit in the CRT is failing. Could be anything, but if your're lucky, it's just a cracked solder joint.

<Insert standard warning about high voltage in CRTs here.>

You could fix it if you know how to wield a soldering iron. Don't bother if you can't. Sell it for parts on ebay and upgrade. It's not paying for a repair.