Game software lockup

[Ponge]

Greetings.

I have been having problems with my PC lately. If I play certain games (Far Cry 4, CoD Advanced Warfare showed this so far), after a random amount of time, the game freezes and becomes unresponsive. There is no error message, and the VGA/CPU does not overheat according to MSI Afterburner. My video card (MSI R9 270X Hawk 2GB GDDR5 PCIE) was faulty when I got it, and it was replaced under warranty. But I susoect it to be causing this problem as this series is known to be faulty.

Question: what (free) software can I use to test/diagnose my PC and to reveal what is causing these lockups?

Thanks in advance.

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