Performance issues with new ram

Feb 8, 2019
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Hey guys! I need your help with something.
So my friend has a pre-build PC, bought 5 years ago. Yesterday he decided to upgrade his RAM from 4gb to 8gb. First he just added the extra 8gb so he could have 12gb. Everything looked fine until he started a game. At the start ( all the games we tested) were running good but they were progressively starting to lose frames. He took his 4gb old ram stick out and just tried with the 8gb one and still the same... We tried to figure it out but there isn't anything clear online...
His specs are:
CPU: I5 4460
MOBO: Asus H81M-k
Gpu: Gt 740
Old Ram: 4GB DDR3 Kingston @ 1600 mhz
New Ram: 8GB DDR3 Hyperx Fury Blue @ 1600 mhz
Also to mention he has the latest GPU drivers installed, runs on win 10 x64. The only thing is that he never updated his BIOS. Could that be the problem? We will try tomorrow because right now he doesn't have a free USB.
Thank you in advance!