bakmi44, since you got this from someone else, the state of the system is unknown to you, so there are some basic integrity checks to run first.

Use the System File Checker tool to repair missing or corrupted system files
https://support.microsoft.com/KB/929833
SFC /SCANNOW

Hopefully it will find and repair something, this is what it looks like after a non-fix successful run.


Then do a disk check, might as well do it for all mounted partitions, but the C drive is the most important. It might require setting a check on next boot, if it asks say yes and then reboot to do the check right away.

Right click on the C partition showing in Explorer, Properties, Tools tab, Error Checking. Do this for the other mounted partitions to make sure they are clean.

If all that comes up clean, or the problems continue, try uninstalling the Asus Gaming Mouse driver, that has been known to be a problem.

Update all of your Windows drivers, and update your Nvidia driver to the latest - at 344.75 now.

The Asus driver downloads for specific laptops, like your G750JZ stop getting updated after a while, so you need to follow the latest hardware releases for hardware of the same type to get the latest drivers, and Asus keeps central locations for many driver groupings that get all the latest driver updates as they get published in specific hardware support areas.

Here is the list of places I look for updates for my G750JH; the best way to get a stable fully functioning G750/G751 is to update all the drivers / apps to the latest Windows 8.1 release.

The G750JW/JX/JH/JM/JS/JZ download areas haven't had new updates for a while, BIOS updates still happen in your model's support area, so check there from time to time.

The G750/G751/551/500/etc share the same basic hardware components; check support download areas for new hardware for newer drivers.

Asus maintains central support areas for hardware component features common to all products, those areas usually have the latest drivers after new hardware releases, sometimes there is a lag before the newer drivers show up there, so still to new product releases support downloads for the latest drivers.

Asus G751 Support / Download areas - Asus hasn't updated all the versions of these support areas, this link discusses the 3 locations were started independantly and not sync'd/updated through to the latest driver releases - check them all to be sure.
http://rog.asus.com/forum/showthread.php?55572-Asus-G751-Support-Download-areas&p=461698&viewfull=1#...

This G751JM/JT/JY/JL download area has the latest drivers of all the G750/G751 support download areas:

G751 Support / Download Areas - Newest - has all 4 G751 models
http://www.asus.com/Search/?SearchKey=g751

G750 Support / Download Areas - Newest - has the G750JY/JZ/JS/JM/JH models
http://www.asus.com/Search/?SearchKey=g750

G750JX - new support location, updates?
http://www.asus.com/Notebooks_Ultrabooks/ASUS_ROG_G750JX/

G750JW - new support location, updates?
http://www.asus.com/Notebooks_Ultrabooks/ASUS_ROG_G750JW/

Here are the latest Asus posted VGA drivers currently 347.25 ; it's better to get the latest from Nvidia - 347.88

Asus doesn't modify the drivers, they release the identical driver packages as Nvidia releases.
http://support.asus.com/Download.aspx?SLanguage=en&m=VGA&p=3&s=111

Notebook Audio drivers - Realtek 7443 - current confirmed to work on G751/G750, some G750 users say 7335 works best for them, if you find a newer release version that works, please let us all know which version and G750/G751 model it works on.
http://support.asus.com/Download.aspx?SLanguage=en&m=Audio&os=30

Notebook Card Reader (realtek) G750 / G751(?)
http://support.asus.com/Download.aspx?SLanguage=en&m=Card+reader&os=30

Notebook Bluetooth drivers
http://support.asus.com/Download.aspx?SLanguage=en&m=Bluetooth&p=3&ft=27&os=30

Notebook WLAN drivers (no Intel)
http://support.asus.com/Download.aspx?SLanguage=en&m=WLAN&os=3

Notebook LAN drivers
http://support.asus.com/download.aspx?SLanguage=en&p=3&s=589&m=LAN&os=&hashedid=n%2fa

KBFilter driver
http://support.asus.com/download.aspx?SLanguage=en&p=3&m=KBFilter&hashedid=n%2fa

Asus Backtracker for Windows 8.1 download
http://support.asus.com/download.aspx?SLanguage=en&p=3&m=Backtracker&hashedid=n%2fa

Asus Backtracker FAQ
http://www.asus.com/support/FAQ/1008640/

Asus SmartGesture
http://support.asus.com/download.aspx?SLanguage=en&p=3&m=ASUS+Smart+Gesture&hashedid=n%2fa

Asus Touchpad
http://support.asus.com/Download.aspx?SLanguage=en&m=Touchpad&os=30

Asus ATK Package
http://support.asus.com/download.aspx?SLanguage=en&p=3&m=ATK%20Package&hashedid=n/a

Asus GPU Tweak for Graphics Cards, currently at release 2.7.9.0 for the G750JW/JX/JH and G751JT/JY
http://support.asus.com/download.aspx?SLanguage=en&p=9&m=ASUS%20GPU%20Tweak%20for%20Graphics%20cards...

Asus GPU Tweak for Laptops, currently at release v1.0.9 for the G750JS/JM/JZ and other new ROG laptops with Optimus
http://support.asus.com/download.aspx?SLanguage=en&p=3&m=ASUS+GPU+Tweak+for+Laptops&hashedid=n%2fa

Here are the Asus posted VGA drivers, it's better to get the latest from Nvidia - currently 347.88
http://support.asus.com/Download.aspx?SLanguage=en&m=VGA&p=3&s=111

Nvidia Drivers direct from Nvidia
http://www.geforce.com/drivers

Asus stopped updating their Intel INFUpdate support area, so go directly to Intel to get the latest chipset INF - currently 10.0.26
https://downloadcenter.intel.com/download/20775/Intel-Chipset-Device-Software-INF-Update-Utility-

For the G750JH/JZ RAID and G751JY PCIE SSD, or if you have implemented RAID, the latest SetupRST.exe is currently 13.6.0.1002
https://downloadcenter.intel.com/SearchResult.aspx?lang=eng&keyword=Intel+Rapid+Storage+Technology+%...

Hopefully this will all bring your Windows install up to date (don't forget about Windows Updates), and you will be stable.

If not, the other choice is to restore Windows to the original out of the box state, by cold booting into recovery mode and select reset to completely reinstall Windows from the Recovery Partition, tap F9 right after pressing the power button until you get the recovery screen. This will completely erase your partitions, all of them, so make sure you have everything you want saved backed up on a disk not connected to the laptop when you do the restore.

I hope the integrity check, Windows Updates, and driver updates solves this for you, please come back and let us know how it works out 🙂