My computer is freezing randomly. But only when I'm playing games.

Freezing under games is most likely due to the increased load put on your processor. If your system is overclocked (fairly likely if it is custom-built) then voltages/settings in the bios need to be appropriately adjusted within safe limits to maintain the overclock. If it is not overclocked than the problem could be due to overheating as a result of inadequate cooling. At the very least get the dust bunnies off the inside of your PC and fan filters. Try temporarily running the games with the computer side panel removed, if this helps then inadequate internal airflow is most probably the culprit. These suggestions are oversimplifications but should get you started.

From the Microsoft article detailing this particular Event ID with a bugcheck of 0:

The Stop error code and the PowerButtonTimestamp are listed as zero. For example, consider the following scenarios:
The Stop error BugcheckCode value is listed as zero. Circumstances can prevent writing the Stop error BugcheckCode information before the computer restarts or shuts down. In this case, a BugcheckCode value of zero is logged. Also, perhaps no Stop error occurred, and the shutdown resulted from a power loss. For example, on a portable computer, this could mean that the battery is removed or completely drained. Or, on a desktop computer, this could mean that the computer was unplugged, or a power outage occurred.
The PowerButtonTimestamp is listed as zero. Circumstances can prevent writing the PowerButtonTimestamp information before the computer restarts or shuts down. In this case, a value of zero is logged. This can occur if the power button is pressed and held for at least four seconds when Windows has an operation running that prevents writing the event to disk. You might also see this scenario if the computer is “hard-locked” and therefore unresponsive to any input, and the computer has to be powered off. To determine whether the computer is unresponsive, try pressing the CAPS LOCK key to toggle the CAPS light on the keyboard.
To check whether this scenario is occurring, press the CAPS LOCK key on the keyboard. When you do this, if the CAPS LOCK light on the keyboard does not change when you press the CAPS LOCK key, the computer may be completely unresponsive (hard hang).

This scenario usually indicates a problem with the hardware. To help isolate the problem, check the following items:
Overclocking: Disable overclocking to see whether the issue occurs when the system is run at the correct speed.
Check the memory: Verify the memory by using a memory checker. Verify that each memory chip is the same speed and that it is configured correctly in the system.
Power supply: Make sure that the power supply has enough wattage to appropriately handle the installed devices. If you added memory, installed a newer processor, installed additional drives, or added external devices, such devices can require more energy than the current power supply can provide consistently.
Overheating: Check whether the system is overheating by examining the internal temperature of the hardware.
Defaults: Reset the system back to the system defaults to see whether the issues occur when the system is running in its default configuration.

If you see that the computer generates a Stop error that contains a BugcheckCode value that is not reported in an event ID 41, change the restart behavior for the computer. To do this, follow these steps:
Right-click My Computer, and then click Properties.
Click Advanced system settings.
Click the Advanced tab.
In the Startup and Recovery section, click Settings.
Click to clear the Automatically restart check box.

Source: Windows Kernel event ID 41 error "The system has rebooted without cleanly shutting down first" in Windows 8, Windows Server 2012, Windows 7, or Windows Server 2008 R2