How to force Windows 10 to use all available RAM?

Question

Windows

Hello, I have an Acer laptop out of the box with 8 + 4 GB RAM sticks. Initially Windows 7 was installed and everything worked ok. But a couple of months ago, I upgraded to a laptop ssd + switched to Windows 10. And I began to constantly receive system errors, that the memory was running out and applications were starting to crash. The task manager shows that only 7.9GB is occupied and 4GB is available. But Windows does not see them? Or don't want to use? Tell me which way to dig.

Answer 1

Apparently the paging file is disabled. Hence the errors.
The paging file must be enabled, best placed on an SSD, the optimal setting is the size of the system's choice.
It is not clear why you decided that the system does not see the memory.