is there HP monitoring software installed?

I’m not sure what you mean by HP monitoring software, but I didn’t install anything on the Mac side of things for my printers. However, I do run Parallels and I have a HP app installed there. I was having trouble with one of my printers (it could have been a really old HP LaserJet 5MP; I no longer have that printer) and was trying to troubleshoot via Windows (there was no utility for the Mac). I haven’t used Parallels much this year, if at all.

I don’t want to get your hopes up, but I had the same behavior when I had Parallels 4 installed. The virtual network devices were causing network drops which stalled Apple mail, Safari, and anything else network related.

Have you tried uninstalling the Parallels software?

I have a MBP 2.66 Ghz Core 2 Duo (over 3 years old) running Snow Leopard.

I haven’t tried removing Parallels. It’s an interesting idea. I don’t often use it, so I could easily do a test removal to see if that helps. Is there any way to tell when these network drops are happening (e.g., something in the logs)?

Try just deleting the virtual network adapters first before deleting parallels. No point in blowing away the whole app yet.

If I delete them (I assume I do this via the Network panel in System Preferences), is there an easy way to get them back? I need to know if this will cripple Parallels for me. I use it to test web sites, and while much of that is done locally, I sometimes need to check the sites when they’re on the server (thus I need internet access from Parallels).

I removed Parallels and there was no change.

Just yesterday I did a full (bootable) backup and then erased the hard drive on the computer & reinstalled Snow Leopard. I’ve been reinstalling software and moving files back into place for the past 2 days. Thus far, only iTunes has locked up on me (about 2 minutes of “Not Responding” before it came back to life).

The only serious problem I’ve encountered is upgrading to iTunes 10. It killed syncing with my Apple TV. I haven’t had time to get on the phone with Apple about this, but it’s clear that I’m not alone. I’d downgrade to version 9 if it were simple to do.

Just in case anyone else suffers the same maddening problems, I’ll post my (hopefully) final update.

After exhausting all of the troubleshooting, I started reporting every crash with Apple (via phone). They set me up with a Genius Bar appointment, during which they sent my Mac in for repairs. They replaced the motherboard.

Things seemed better initially, but then the crashes started up again.

Another series of phone calls, and another Genius appointment. This time they replaced the motherboard (again) and the card with the power and USB ports (sorry, don’t remember exactly what this was called; I can look it up if it’s important).

Since the second repair, it’s been stable.

So, in the end, it was hardware. Thank goodness I paid for Apple Care (though if I had pursued this aggressively when it first started happening, I would have been within the first year of coverage).

Thanks for everyone’s help.

Glad they solved it!