PC not powering down!! Please help...

After using my pc for about 5-6 hours and then try to shutdown, everything turns off except the PSU, which leaves the system fans, cpu fan and cdrom drives on and the only way to turn my computer off is to hit the switch at the back of the psu. I have tried every windows shutdown trouble shooter on the web and replaced a motherboard and PSU but the problem is still there…

After a few weeks of experimentation I noticed that the shutdown problem occurrs only when the sensor chip on my motherboard stops working and no longer updates the system voltages etc.

Please if anyone has had this problem or any ideas reply.

My system hardware:
Winfast NF4k8mc-ers (nforce4) motherboard
Antec Tp2 480w psu
AMD64 3800+ venice
nvidia 7800gt
160gb WD hd
1G pc3200 ram

How long does the power supply stay on? Is this after Windows has shut down?

[QUOTE=Big B]
How long does the power supply stay on? Is this after Windows has shut down?
[/QUOTE]

It stays on forever if I dont turn it off by hand, and yes this is after windows has shutdown and the monitor is also on standby (but the gpu fan is still on, as is all the other fans).

sounds like a motherboard problem

I’m not familiar with that motherboard, but it’s possible there’s either a BIOS setting that controls this, or a bug in the BIOS. If it’s not one of those two, there may be something with the particular power supply model you have that has some odd quirk or setting that does this—although I’m not aware of any such issue with Antec power supplies. Doesn’t mean it couldn’t exist.

i agree with Big B
i would probably reset the BIOS, and hope that sorts it out