I replaced the internal hard drives in my PowerMac G5 (dual core 2GHz, Mac OS X 10.5.8) over the last bank holiday weekend.
Ever since it's been a bit slow to shut down compared with before (takes about a minute where it used to take about 10 seconds).
This morning it hung when trying to shut down. The desktop cleared and I was left with a screen showing the desktop pattern with the spinning cog wheel. After 5 minutes I forced a shut down using the power button as I was going to be late for work.

Any ideas what could have cause it?
I'm planning on zapping PRAM and resetting the SMU/SCU and checking my login items to see if there is anything that could be causing a problem.

Any other suggestions on things to try?

Do you have a home network with resources that could be being accessed at the time of shutdown?

Mark

Try a Safe Boot (that's starting up with Shift key held down) which does some disk checks and clears certain caches. You should get to the OS X log-in screen eventually (it will take a bit longer than a standard restart), log-in to your normal account then shut down and start up as normal.

If no better, try downloading OnyX and running all the options under its "Automation" tab, in particular the cache clearing options and resetting Spotlight (it could be stuck on the SpotLight process trying to index your new drive(s).

If it continues, check all hard drives in Disk Utility, and immediately on startup after a force shutdown - also launch Console first thing and check the "system.log" for any clues as to what's hung the shutdown process. My guess is some background process, maybe software drivers for a scanner/printer/USB device, etc. Check all drivers are up to date for USB/Firewire devices.

Thanks for the responses folks.

The only thing on the network is the broadband router and a printer (that was switched off anyway).

I've reset the SMC controller (unplugged for more than 2 minutes) as instructed on the Apple support pages.
Did a safe boot (no problems with shut down) and checked the start-up volume with Disk Utility (no problems)
I've checked Console>system.log:


Everything before that was several minutes before so I assumed it wasn't affecting the shutdown command.
I've un-installed the Wacom tablet driver as I disconnected the graphics tablet to do the hard disc upgrades and didn't bother to reconnect it (don't use it very often).
Fingers crossed.

The only other thing I recognise in that list is mDNSResponder, which is a background process related to Spotlight indexing. Now, it could be that Spotlight was updating the index when you shut down, but if it continues then I'd use OnyX to reset the Spotlight index (under the Automation tab) - next time you restart it will re-index your new hard drives again.