Tksiu1977
Driver and BIOS update forget?
Windows 8,1 driver DV7 series
New BIOS
New UEFI
Intel Management Engine Interface Driver
Intel Rapid Storage Technology
Ralink Wireless Network Controller Driver
Realtek Local Area Network (LAN) Driver
for your problem, install after driver update INTEL HD reboot and install Nvidia
intel® Iris™ and HD graphics Driver for Windows 8.1
https://downloadcenter.intel.com/Detail_Desc.aspx?lang=eng&changeLang=true&DwnldId=23405
Nvidia
http://www.nvidia.com/download/driverResults.aspx/70187/en-us
and you have normal speed