iis 7 worker process hangs

From my diagnosis the worker process stops responding randomly, the server becomes 0% cpu utilization because the w3wp.exe process stop responding to the requests.

At this time, no websites respond, I have to restart IIS in order to make it work. Mostly the IIS restart  not work (error stating services are not responding) and I have to restart the entire server. and I have to do that 3 times a day

I have about 150 Application Pool Created , and the server content 6GB of RAM

I don't understand way application pools Hang !!. I have installed DebugDiag from Microsoft.com & created dump files however unable to understand what the analysis results are that mention max time consuming threads etc.

- Server - 6GB of RAM
- Windows Server 2008 SP2
- only IIS 7.5 running in the server


Thank you so much for reading through my issue. You help will be greatly appreciated.