I have a dell Xps 720, I have been getting a keyboard failure on boot up, the diagnostic lights on my desktop say 234 which is a USB failure according to the dell manual. I have read on many other post that a keyboard failure on boot up has to do with the motherboard. However my problem differs from them as I can boot up to windows by unplugging all the usb cables. However its getting on my nerves to constantly unplug and plug in the USB's. Recently my keyboard has been lagging typing and its been going off at random times regardless if its plugged in. So my question is, is it my keyboard or my Motherboard?
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Sounds like a bad keyboard or failure of a USB device, not a bad motherboard.
Swap out your keyboard with another one and try again.
Replace they keyboard, try a BIOS reset as well (will be a jumper on the motherboard for that).