Holy crap – hate this type of thing.
My big sharepoint site stopped responding, and just got HTTP 503: Service Unavailable errors.
Can’t even get into Central Admin pages, because – guess what – they run on Sharepoint too.
Checked everything and googled around for a while before I found this blog article that made me think to check the APPLICATION POOLS. For some reason they’re not set to restart automatically.
Weird that even an IISRESET and a Reboot didn’t fix the problem though. I had to go into INETMGR and Start the AppPools manually.
Article from Matthew Churilla: