Application pool keeps on stopping

Thanks for your reply.

There have been no password changes.

the only thing which i found in uLS logs was:

User Profile Application Proxy failed to retrieve partitions from User Profile Application: Microsoft.Office.Server.UserProfiles.UserProfileApplicationNotAvailableException: UserProfileApplicationNotAvailableException_Logging :: UserProfileApplicationProxy.ApplicationProperties ProfilePropertyCache does not have d9eb0a1a-25ca-44b5-a553-d45f572e12dc   

 at Microsoft.Office.Server.Administration.UserProfileApplicationProxy.get_ApplicationProperties()   

 at Microsoft.Office.Server.Administration.UserProfileApplicationProxy.get_PartitionIDs()   

 at Microsoft.Office.Server.Administration.UserProfileApplicationProxy.IsAvailable(SPServiceContext serviceContext

Application error when access /dept/TO/DC/_vti_bin/client.svc, Error=The server was unable to process the request due to an internal error.  For more information about the error, either turn on IncludeExceptionDetailInFaults (either from ServiceBehaviorAttribute or from the <serviceDebug> configuration behavior) on the server in order to send the exception information back to the client, or turn on tracing as per the Microsoft .NET Framework SDK documentation and inspect the server trace logs. 

I found the following error logs in event viewer:

A process serving application pool '96eb1b47a3694bbd99fd7d148ab4151d' failed to respond to a ping. The process id was '24976'.

Application pool '96eb1b47a3694bbd99fd7d148ab4151d' is being automatically disabled due to a series of failures in the process(es) serving that application pool.

A process serving application pool '96eb1b47a3694bbd99fd7d148ab4151d' suffered a fatal communication error with the Windows Process Activation Service. The process id was '11892'. The data field contains the error number.

Application pool SecurityTokenServiceApplicationPool has been disabled. Windows Process Activation Service (WAS) encountered a failure when it started a worker process to serve the application pool.