Application Pool stops by itself

Hi, 

We are using NopCommerce 3.2 and Alfresco Template for it. We have a problem that application pool on our site stops by itself and the site can not be loaded until we manually start it again. We moved from Personal Class server to Business Class thinking that it is a memory issue, but the problem persists here too. Looking at the control panel this what it says regarding the working memory if that helps you recognize the problem.

Process Info {2 processes)
PID/Name:              522808 - w3wp
Start/Uptime:          6/19/2015 4:48:17 AM - 00:07:06
CPU Time:              00:10:17
Working set (memory):  949.85 MB


PID/Name:               159836 - w3wp
Start/Uptime:           6/19/2015 4:54:00 AM - 00:01:22
CPU Time:               00:01:42
Working set (memory):  443.78 MB


Has anybody had a similar issue or has any idea how to resolve and isolate the problem, thanks!

by the way I am looking at our other site on the same version of NopCommerce and with a same template that works well, and it has only one process running 

Process Info
PID/Name:          323380 - w3wp
Start/Uptime:      6/18/2015 5:56:36 AM - 23:26:44
CPU Time:          00:07:38
Working set (memory):  453.89 MB