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Windows 7: Unknown Device

27 Aug 2011   #11

Windows-7 Professional 64-bit


"Unplugging the motherboard from the AC source...", per my post, is the same as unplugging your system's power cord from the wall. The point is to remove the AC juice that is trickling to the motherboard which is not the same as shutting down your system. There is no need to unplug and re-plug all your USB devices. Sorry if I wasn't very clear. Thanks.


My System SpecsSystem Spec
08 Jan 2012   #12

Windows 7 64bit Ultimate

Just had the same thing happen. Couldn't find my "Unknown Device" because there wasn't one lol

Shut down system
Removed AC power for 30 secs
Problem gone, no more Unknown Device pop-ups and nothing showing "Unknown Device" in the Devices & Printers window.

How crazy is that...!

Knew I'd find the answer here though. Cheers!
My System SpecsSystem Spec
13 Jul 2012   #13

W7 Ult 64
Thank You

Problem after installing 7 port USB hub.
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18 Jul 2012   #14

Windows 7 x64

Do you have to really unplug the motherboard? Or can you just press the switch?
What is the AC power even? I'm really bad at this...

I tried switching the power and unplugged the power cable but it didn't work for me. I still get the "Unknown Device"
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18 Jul 2012   #15

W7 Ult 64

Quote   Quote: Originally Posted by Lionboy View Post
Do you have to really unplug the motherboard? Or can you just press the switch?
What is the AC power even? I'm really bad at this...

I tried switching the power and unplugged the power cable but it didn't work for me. I still get the "Unknown Device"
No mother. No switch. While up and running, select normal shutdown and wait until the computer shuts down. Then unplug the power cable. Wait 30 seconds. Plug in the power cable. Restart the computer. Hope.
My System SpecsSystem Spec
11 Oct 2012   #16

Windows 7 pro 64 bit

I had a similar problem with my Dell XPS 9000 but mine was a slow process of the USB ports going bad. It started out as a slight annoyance where I had to wait about 15 seconds after Windows appeared before the mouse or keyboard would work so couldn't log in without waiting for the USB mouse and keyboard to be active. Well, it finally got to where it took 2 or 3 minutes and sometimes it never saw my mouse or keyboard. To make a long story short, I tried everything in the thread above short of changning the motherboard and nothing worked. I had an error in Device Manager show up under the USB drivers. I finally decided before changing the mother board I'd re-program the BIOS with the Dell firmware file downloaded from their site. The version was identical but apparently something got corrupted in the BIOS and the refreshing of the firmware did the trick! Device Manager was happy and the mouse and keyboard work with no delays.
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27 Apr 2013   #17

Windows 7 Ultimate x64

OMG Thank you!!!! After unplugging everything USB I could think of and not getting successful results, I finally stumbled upon this "silly" solution and I just want to say a HUGE thank you to whoever provided the solution. Not only did switching off the power switch and disconnecting the AC cable resolve this issue, but it also resolved an issue I had with devices gone missing from my Devices and Printers window, more specifically those related to Bluetooth.

So glad this forum exists!
My System SpecsSystem Spec
11 Feb 2015   #18

Windows 7 Professional 64-bit

I am still continually amazed at how "unplug it and plug it back in" solves a plethora of problems, especially the ones that MS over-addresses and fails with. It's usually the problems that I take the most exhaustive measures to diagnose that are solved by "turn it off, and turn it back on". Kind of pathetic...and frustrating. Thanks to all of you in this forum. My problem...SOLVED!
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20 Jul 2015   #19

Win7 Pro 64bit

I can't believe this fixed my issues too: was having problems with my bluetooth adapter, wasn't visible anywere but there was an "Unknown USB device". Unplugged my power cable, plugged it back on, restarted the laptop, bluetooth adapter automatically detected & installed, problem solved
My System SpecsSystem Spec
09 Sep 2015   #20

Win 10 Pro 64bit

Thank you so much, I was about to cry seeing this error in windows 10 just randomly one day(everything was working flawlessly for past few weeks)and having second row of USB ports on the back of Asus Rampage V extreme motherboard not working at all. At first I thought my new Logitech G910 keyboard has just died.
Not having much luck,Just had Asus Rog swift die last week and now I thought oh no my MB is now on the way out, Was ready to pull everything apart and decided to google problem and stumbled onto this post.
I can't believe this actually worked, But it did!
Usually when I have router problems a good switch off at power point fixes it, I never thought that a USB problem would be fixed like this so I never bothered trying.
Thanks again you have made my day and saved me so much hassle of RMA'ing a motherboard which is the worst, Removing all the parts.
My System SpecsSystem Spec

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