Fan comes on when power is off?

[AnitaE403]

My Dell computer, Windows 8... was completely powered off... in the middle of the night I wake up because its fan is going at full speed. The monitor is flashing and power is going to two (out of three) external hard drives.

When I turn the computer on, the fan stops and everything seems to be working normally. As soon as I turn the computer off the fan comes on sounding like a jet engine and two out of the three external drives are flashing. The only way to stop it is to either turn the computer back on or unplug the power.

Whats going on?

 

[asvent]

The exact problem I can only speculate on, but all the possibilities that come to mind involve hardware replacement as being the solution. So assuming the unit is under warranty, make a warranty claim with Dell.

 

[AnitaE403]

The exact problem I can only speculate on, but all the possibilities that come to mind involve hardware replacement as being the solution. So assuming the unit is under warranty, make a warranty claim with Dell.

Thanks... I did call Dell and they're sending an onsite technician with parts. They mentioned replacing the motherboard, power supply or fan. The diagnostic tests didn't indicate what the problem might be.

 

[Itaregid]

I would not assume hardware just yet or else not sure the computer would work normally when you manually start it. Have you scanned for malware? Have you checked Task Scheduler to see if something is set to run in the middle of the night, like an auto-updater, backup program, Windows Update, or your malware scanner running scans or checking for new updates.

The BIOS Setup Menu has many "Wake on..." options that can be doing this, including Wake on LAN. If Wake on Mouse or Wake on Keyboard are enabled (and those two normally are) a wandering cat or other pet can start up the computer.

 

[asvent]

I would assume hardware if this happens when the computer is otherwise turned off. Malware would require the computer to be turned on to operate. As the OP stated in the first post, this happens immediately after the computer is turned off, not just in the middle of the night. To me that says bad motherboard. Some component isn't regulating power correctly in the off state. PSU is also plausible, but the fan is just grasping at straws. Still, Dell doesn't want to have to pay to send someone out a second time so it's easier to just load them up with everything even remotely plausible and just have the tech send back whatever they don't use.

 

[Itaregid]

I am just saying, I don't assume anything. And I would look at other causes (that are free to check and verify) before looking at hardware. Electronics does not turn on by itself. Something must be signaling it to turn on.