Where is the cmos jumper on this model X751NV

Don't know about the cmos jumper location but an image of the motherboard (see below) shows that it has an RTC (Real Time Clock - aka cmos) battery holder on board.

(click on image)

To reset the BIOS back to factory default settings, except for admin password (a cmos reset doesn't reset the BIOS password).

Open the laptop and disconnect the main battery from the motherboard. You don't have to remove it, just disconnect it.
Remove the RTC coin cell battery from the motherboard (when it is out, check its voltage with a meter. If it is <2.5V DC replace it. The battery model number should be printed on the battery).
Press and hold the laptop's Power on/off button for a full 30 seconds and then release it.
Reinsert the RTC coin cell battery on the motherboard (usually it is +ve on top as marked on the battery).
Reconnect the main battery to the motherboard.
Re-assemble the laptop, connect the charger and then try turning it on etc.

If it turns on OK there may be a message that the date and time is incorrect. This is normal as the BIOS has been reset. After the date and time have been corrected, the message won't appear the next time the laptop is started. Also if any user definable BIOS settings were changed to suit whatever operating requirement you had, they will have to be changed to what you had as they also have been reset.

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I havn't battery in my motherboard

ARTOGAL LAGOTRA 의 2023년 2월 12일

In my motherboard there is not the battery... Where I can find the cmos please

ARTOGAL LAGOTRA 의 2023년 2월 12일

@ARTOGAL LAGOTRA

Does the top of your motherboard look like the image I posted?

If not the battery might be on the underside of the motherboard, so you will have to remove the board from the laptop

jayeff 의 2023년 2월 12일