What should I do if I get the message "The system is running out of free resources"?

Question

Windows

Good afternoon!
On a Windows 7 computer, a pop-up window has recently started to appear with the text "The system is running out of free resources. Too many programs may be running." and one single "OK" button, when pressed, the window closes.

No detailed information can be seen, this warning appears randomly, regardless of the number of applications running, there is nothing completely loaded in the task manager. There is nothing in the text of the message in Google. We thought it was some kind of virus, but the virus scan did not reveal anything.
Can you please tell me what could be causing this warning? And what to do?
Thank you!

Answer 1

Memory is running out, operational.
You can view it not with the standard task manager, but with my favorite program - Process Explorer from Sysinternals

Answer 2

See in the Task Manager what process / sy are eating up resources