ThinkPad T42 randomly goes to sleep

[PiZzA EnGiNeEr]

I have a ThinkPad T42 with the Radeon 7500 that has an issue of randomly going to sleep. It seems to happen after the machine has been running for half an hour after a cold start. The laptop will boot, operate normally and then randomly go into sleep mode. It will do it in Windows, sitting in the BIOS or at a DOS prompt with PC doctor. I figure it has something to do with cooling and I've replaced the CPU and the CPU heatsink/fan and the machine still does it.

Is this a GPU problem? The machine is a later 2005 model with the red dots around the ATI chip. The video itself works fine and shows no signs of distortion or flashing colors. Any help on this problem would be appreciated. Thanks

[poshgeordie]

Can you say how you know / think it's going to sleep.
Does the hibernate (moon) symbol light?
Does the screen go blank?
Does the same thing happen when it's connected to an external monitor?
Does there still appear to be hard disc activity - does the HDD light still flash for instance?

If you press on the palm rest just to one side of the Trackpad does the display reappear?

[PiZzA EnGiNeEr]

The moon LED comes on and the machine enters standby. I can always wake the machine up by pressing the power button. The hard drive activity light says off when it's stuck in sleep. I've tried it closed lid with an external monitor and the machine still does the same thing.

Recently now in the last day it's got worse. The system will completely power off randomly without touching it. It will do this running bare bones (no batt, 256mb of ram, no cdrw/hard drive or wifi card) just sitting in the F1 bios. I'm guessing the board is junk but are there any know board-level repairs to fix this problem? It sounds like a bad thermal sensor to me.

[GomJabbar]

If the moon LED comes on, then that means that you are in 'Suspend to RAM', not 'Hibernate to disk'. You should be able to press the Fn key to get out of Suspend to RAM. Sometimes you might have to hold the Fn key down for a few seconds for it to work.

It is possible your computer is going to sleep if your battery is dying or your battery charging circuit has a malfunction. Try removing the battery and just running on AC power for a test.