Is the computer plugged in? Playing games under battery power will frequently cause to "power save mode" and maybe that's what you're seeing..
If your computer is plugged in, but not charging, that also could explain part of the problem. It appears like you may have forgotten a step in battery software renewal procedure. Try ALL of the steps in the instructions below and see if it helps.
Uninstalling and reinstalling power management software
In order to correct problems with the battery's power management software, follow the steps below.
1. Access the “Device Manager” .
2. Expand the Batteries category.
3. Under the Batteries category, right-click the Microsoft ACPI Compliant Control Method Battery listing, and select Uninstall .
WARNING: Do not remove the Microsoft AC Adapter driver or any other ACPI compliant driver.
4. On the Device Manager taskbar, click Scan for hardware changes .
Alternately, select Action > Scan for hardware changes .
Windows will scan your computer for hardware that doesn't have drivers installed, and will install the drivers needed to manage your battery's power. Restarting Windows will have the same effect of letting Windows re-recognize the hardware and installing the correct drivers.
If that doesn’t fix it, then shut down the computer, unplug all power cords, remove the battery, then depress the power button for 30 seconds. Replace the battery making sure all connections are solid, then plug in the power cord. Hopefully things are good.
And if this is repeatedly happening, where it's not charging correctly, then I'd certainly check to make sure you've got all the right motherboard/chipset drivers and BIOS updates for your machine.
Hope this helps.
Grif
Hello Everyone so my laptop just slow down this evening when i'm playing video games on my Asus Laptop. I Checked CPU-Z and the Multiplier And Core Speed (From The Clocks Section) is really low when playing games. I don't get this problem when just surfing or playing music just playing games like GTA 5, Saints Row 4 etc... I Tried Uninstalling and re-installing "Microsoft ACPI-Compliant Control Method Battery" in Device Manager (From This Reddit Post) but this dosen't work anymore someone help. I don't want to downgrade windows.
Screenshots Below
(With Game On)
(Difference With And Without Game[left without game, right with game])

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic