Windows low on Memory - Pc running slow - possible failing RAM -

My PC has started running really slow from time to time and crashing when I try to do simple tasks. I keep getting this pop up. (screenshot below) It is not all the time but has started getting more and more frequent.

I get it when just using one program at a time and sometime even when it is sitting idle. I have ran Malwarebytes and other antivirus/malware software and there seems to be no infection. I only have Eset installed and running so its not loads of antivirus trying to compete or hogging the RAM.

I have closed unnecessary apps and programs and I still have the same problem. There is 3GB of DDR3 (1x1GB + 1x2GB sticks) installed. Could one of these be failing?

Is there a way to check the RAM, like a disc check, using CMD. I have seem an app online called "memtest86" but not sure if this is OK or good to use. Can anyone help please and suggesting a fix or solution.

I have also attached a sreen shot of CPUz and the task manager. The screen shot is taken as I make this thread with nothing else open only Firefox, Snipping tool. It seems to run about that all the time now, even when sitting idle.

Any one got any ideas?

Thanks

Graemzy

I've seen that happen if the pagefile is too small so check pagefile settings for your windows partition.