Is my ram or gpu unstable?

Jan 13, 2019
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So i recently built myself a computer and i have overclocked the ram, cpu and gpu.

My PC was a budget build and it includes a MSI Radeon RX560 aero itx gpu and corsair vengeance lpx 1x8GB DDR4-2400 ram. My ram speed has been overclocked to DDR4-3000 and the gpu frequency is increased by 14.5%, gpu power limit increased by 15% and the gpu memory frequency to 1850MHz. The gpu was overclocked in the AMD Radeon Software. I have ran memtest and multiple MSI Kombustor windows to test the stability. I encountered no issues in the tests but now i have started playing Assassins Creed Syndicate on my PC and just had my screen lose signal and all sound stop for a droning type sound I had to restart my PC and nothing us broken although now i don't know if my ram or gpu is unstable. Is it even my ram/gpu or is it something like the old laptop drive 5400rpm i took or even the cpu (I also ran IntelBurnTest and prime95). I have no clue what to do considering this is my first build and it is starting to bug me. I also ran into the same issue on Shadow Of The Tomb Raider and my thermals are fine so what could be causing this?