Leopard 10.5.1 Freezes

Does anyone else have this problem (and a solution)? I leave my MacBook powered up and plugged in at home to go run some errands. No screensaver enabled, Energy Saver set to "Put to sleep - never" and "Put display to sleep when computer is inactive - 15 minutes" and hard drive sleep - never. When I return an hour or so later, the screen is dark and the white light on the front edge of the keyboard is glowing. I move my finger around the trackpad and the screen stays dark. I hit various keys on the keyboard and the screen stays dark. Eventually, I press the power button figuring I'll have to reboot. Suddenly the screen comes back, but everything is frozen and a dialogue box with the "Are you sure you want to power off? Yes No Cancel Whatever" is there. Of course no trackpad and keyboard functionality so I have to hold the power button down until the whole thing goes dead and then reboot. This doesn't seem like a good thing to me. Any ideas? Thanks in advance!
Dave

Do you have any external devices plugged in? Does this happen with all user accounts, or just one? Has it always done this?

Best thing I can suggest is to Google it. Try:

leopard freeze

as a starting search, and modify it as needed. My guess is your problem isn't unique, even if it isn't widespread. Someone else has encountered it I'm sure, and probably has even posted much more about it.

I found a couple thing on a quick search. Did you get your machine with Leopard pre-installed, or did you upgrade? If the latter, what kind of install did you do? If you did something other than an Archive and Install, you might want to look at this link:

http://tech.monstersandcritics.com/news/article_1369877.php

Good luck!

I have that problem on my MacBook Pro, and I am running 10.4.11. The only difference is that mine unfreezes after about 2 minutes. This only happens sometimes though.

This seems to be a new occurrence since installing 10.5.0 on both the MacBook and Mac Mini. They also are both now running 10.5.1 since it's release, though the problem was present before that. The MacBook connects to the network via AirPort Extreme card and my AirPort Extreme base station has "wireless g/n" setting turned on so my iPhone will connect.
The MacBook mounts two external drives (320GB for Time Machine & 750GB for media files) that are connected to my Mac Mini which is plugged into the Airport Extreme base station via gigabit ethernet. The HDD's connect to the Mini via FW400 and USB 2.0 respectively. Does this ring any bells with anyone?
Both Macs have the same 2 user accounts: mine and my wife's. Both are administrator accounts. She is generally "permanently logged into the Mini and I am generally "permanently" logged on to the MacBook. Both users are generally logged on to both machines via fast user switching as well, but with nothing other than a browser running in their respective sessions.

I did an archive and install of Leopard on both Macs from 10.4.11 with no issues other than this.

Try making a new, "clean" user account and see if the problem continues to occur. You should also look over and maybe uninstall any 3rd-party add-ons that may be running from or have files installed somewhere in /Library since those would affect "All Users". Also be sure anything you do have installed is compatible with Leopard.

Worst comes to worst, try making a new partition and installing OS X with a new user (import nothing, install nothing). If the problem continues to occur even when booting from that, then you can pretty much figure the problem is hardware, or some bug with Leopard and that particular combo of hardware.