There is no download for a Mac OS X installation disc. You should connect any USB keyboard while trouble-shooting this problem.
it shows a fold icon in the middle and that's all.
That means the iMac cannot find a bootable system. That often (but not always) means there is a problem with the internal hard drive.
You can try a few things. First, reset PRAM
It should work with a Windows PC keyboard, using Windows and Alt, instead of Command and Option.
If that does not help, use this procedure to reset the SMU (power management)
When you do this, if you have been using a "power strip," try connecting it directly to a wall outlet by itself. Disconnect everything, and initially power it up with only the power cord connected. If it starts up normally, connect only keyboard and mouse. Use it that way for a while to see if any problems come up.
If the problem still recurs, you'll need to have a Mac OS X installation disc (for the currently installed version of Mac OS X) to do additional trouble-shooting on the hard drive.
bc i have pc keyboard so it's hard to find the right key.
So i managed to get into Open Firmware then i type:
then it says OK
then i can see two lines with the last words OK each line then the imac restart itself.
That's all i can do...
is there any command that i can run to check HDD or check hardware?
The general hardware test is on the disc that comes with each Mac model. You can't run a test of the startup disk, unless you can start up from a system and run Disk Utility. If your normal system is not working, you would need to start up from the optical drive with a Mac OS X installation disc, and run Disk Utility from there. And you don't have one...
Be sure to try the SMU Reset procedure (linked in previous post), in case there is some power issue that is keeping the hard drive from working properly.
If you have another Mac with FireWire, you can start up your iMac G5 in FireWire Target Disk Mode, connect it to the other Mac using FireWire, and use the other Mac to run Disk Utility on your iMac G5's hard drive. This is the FireWire Target Disk Mode procedure.