Then obviously you've a hardware problem if nothing software related solved it. If you claim he hasn't changed anything (ie. reinstalled GTA and MTA) then you've a physical issue with your RAM memory. Judging by the fact you still use Windows 7, you've an older system (probably DDR3 perhaps even DDR2 memory). Finding replacement DDR2 RAM sticks is next to impossible at least where I live, not sure about you. Replacing DDR3 memory is still doable you just have to find the correct memory specs (frequency, amount that is supported by your motherboard, etcetera).
Oh and if you've malware you won't be able to reinstall Windows 7 with proper security patches as the support for Windows 7 was discontinued in 2020, so if it is actually a Windows related issue, and your hardware is weak, you're gonna have a hard time fixing that without crippling your computer.