Windows XP doesn't always boot successfully

The problem is this: my work PC sometimes doesn't boot properly. What happens is that it'll boot up happily, but at the point where it should switch to the XP-theme for the logon prompt, it doesn't -- it just says "Windows is starting up" and takes a long time (minutes) to get to the login prompt.

When you do log in, it takes just as long to get to the desktop, and nothing works properly. Event Viewer will start up, but doesn't display any events. There're no network connections in the relevant part of Control Panel.

After several (five or so) cycles of shutdown-and-restart, it will start up perfectly happy, as if nothing has happened.

Now, this has never happened on any of my other machines, but also happens occasionally on other PCs here at work.

My PC specs:

Dell Precision 470 Workstation, with 2Gb RAM, dual Xeon 3.0GHz HT CPUs, 2x80Gb SATA disks (JBOD). ATI FireGL graphics.

It seemed to start happening during installation after I joined the domain (AD-based, I think we're still in W2K compatibility mode), and would happen almost every time I rebooted.

It hasn't happened for a month or so, but just started happening this morning. As I type this (on my laptop), it's still happening.

Ideas?

Look for network issues or roaming profiles. I know there were a few bugs where it would try to load (or save) roaming profiles and fail, causing a very slow boot (or shutdown).

Otherwise, check to see if your domain admin folks are dumping large amounts of "updates" or "pushes" to your system. That is something I see a lot of here.

Lastly, make sure you have a local machine admin account. Try logging in with that, shutting down, restarting and use this account to try to diagnose. If it is getting hung up on a network or domain issue, this might help clear it.

Thanks for the suggestions. More information below.

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Look for network issues or roaming profiles. I know there were a few bugs where it would try to load (or save) roaming profiles and fail, causing a very slow boot (or shutdown).

We don't use roaming profiles.

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Otherwise, check to see if your domain admin folks are dumping large amounts of "updates" or "pushes" to your system. That is something I see a lot of here.

Nope, this reboot was due to Windows Update, but it's been fine for the last few weeks.

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Lastly, make sure you have a local machine admin account. Try logging in with that, shutting down, restarting and use this account to try to diagnose. If it is getting hung up on a network or domain issue, this might help clear it.

I'm logged into it now. And it's very odd.

If I go into Event Viewer, I get a message box: "Unable to complete the operation on 'Application'. The interface is unknown.

If I right click on "My Network Places" to get to the Network Connections control panel, there are no interfaces listed in there. ipconfig shows both interfaces correctly.

Plugging in the network cable (it was unplugged, to eliminate dodgy DHCP servers or other network problems) and running ipconfig /renew gives me "An error occurred while renewing interface Local Area Connection : The RPC server is unavailable."

Going into Computer Management and clicking on "Device Manager" doesn't show anything. Trying "Performance Logs and Alerts" hangs up Computer Management.

Browsing around in the registry doesn't show anything obviously amiss.

"sc query" shows nothing -- as if no services were started.

I'm going to try a boot into Safe Mode, to see if anything is obvious there, but it's not good.