[Cowdude]

This Mac after warmed up and fan goes up , if restarted or shut down and started, will go to a gray screen, with a grey apple, but no pinwheel. After a couple of minutes the gray apple turns to a O with a \ through it. After unpluging to shut it down and waiting a couple of hours(it seems to have to cool down), it starts right up.
I've used Techtools Pro 4.5.2, and everything passed. I've used Hardware Monitor 4.11 but this Mac only shows temp sensors for the two internal S.M.A.R.T. hard drives and nothing else.
Can temp sensors be replaced or reset? Any way to check cpu temp? How can I check the heatsink?
Anything you can think of would be of help, Thanks.

[wubrew]

Temperature Monitor: Description
That's the software site. I do not think it is the temp issue. looks like time for you to archive and reinstall the OSX.

[Cowdude]

I have OSX 10.4 on both harddrives. When problem starts, I restart with Option key down, the screen shows both harddrives with blessed folders, plus the Techtools edisk, and the Techtools emergency disk in the DVD. But with any of the disks choosen, it stills shows gray screen, with gray apple that eventually turns to O with \ through it. Once turned off and cooled down, it starts right up.