Microsoft Explorer Error Whilst Gaming

Had a "Your computer is low on memory. Save your files and close these programs" (Civilization 5 for the past 2 days, it crashed once, and a popup 5 minutes ago whilst playing the newest Sniper Elite release. From what I understand Civilization uses a lot of CPU power but Sniper elite? On the low graphics settings preset? and these few errors only started happening maybe a week ago. The only hardware change that I made was adding a SSD. Not really looking for a fix just what is the cause? My computer was only using 1.58GB of memory and I have 4GB.

 

Windows 7 Ultimate 64-bit SP1

AMD Phenom X3 8450

Toliman 65nm Technology

4.00GB Dual-Channel DDR2 @ 401MHz (6-6-6-18)

OEM_MB NARRA3 (Socket AM2 )

2047MB NVIDIA GeForce GTX 650 Ti (ZOTAC International)

112GB KINGSTON SH103S3120G SCSI Disk Device (SSD)

466GB Western Digital WDC WD50 00AAKX-22ERM SCSI Disk Device (SATA)

 

 

I'm a forum n00b so heres a link, to a screenshot, of the most recent error xD

http://imgur.com/1AVX1wW