Application pool is not running (4277262)

What can I do when an application pool in a SharePoint farm being monitored by Diagnostic Manager is not running?

Below are some troubleshooting steps to analyze and investigate the issue:

1. Get PID of the application pool's worker process. For methods on how to do so, please click here.
2. Open IIS Manager, expand Application Pools, select the affected application pool and click Advanced Settings. On the Recycling section, expand "Generate Recycle Event Log Entry" and enable the following attributes to get as much information as possible:
    

   Application Pool Configuration Changed	Event is logged when the application pool recycles due to a change in its configuration
   ISAPI Report Unhealthy	Event is logged because an ISAPI extension has reported itself as unhealthy
   Manual Recycle	Event is logged when the application pool has been manually recycled
   Private Memory Limit Exceeded	Event is logged when the application pool recycles after exceeding its private memory limit
   Regular Time Interval	Event is logged when the application pool recycles on its scheduled interval
   Request Limit Exceeded	Event is logged when the application pool recycles after exceeding its request limit
   Specific Time	Event is logged when the application pool recycles at a scheduled time
   Virtual Memory Limit Exceeded	Event is logged when the application pool recycles after exceeding its virtual memory limits

3. Review and analyze System event logs on the IIS server.

For additional information about application pool recycling, please refer to the following:

IIS Application Pool Recycling
Managing Application Pools in IIS 7