Check your RAM for defective sticks, with Memtest86 memory checker
Memtest86 checks 32 and 64 bit system memory to find problems with installed modules. It is common knowledge that Memtest86 is a free and one of the best if not the very best application of this kind.
Memtest86 works really fast, you won’t have to spend a lot of time to test your RAM, and it gives reliable results.
If you guess that a malfunctioning PC suffers memory problems, since everything else seems to work fine, the PC is clean from dust, temperatures are normal, etc., make a bootable USB drive, provided by the program, and let Memtest86 clean boot and test your RAM modules.
Of course Memtest86 is not compatible with any single RAM stick available, but most probably it won’t face problems to test yours. Memtest86 includes options that regard expert technicians. You can ignore these and use the standard settings. Note that commercial versions of Memtest86 are even more powerful. Just start with the free one, and see if it works for you (in most cases it will).