That is very strange. If you trash the preferences, a new one should be created when you next launch Logic.
Okay, might be a bit late to check, but did you make a copy of your preference file before trashing it?
Copy it back, launch Logic and see if you have sound.
If you start a new Logic project do you still have problems? With delays and CPU going high?
Or is it only projects you have been working on that have the issues?
I'm very concerned why Logic didn't create a new preference file when you launched it.
Maybe re-installing Logic is the way to go.
Here the info from the Apple support site on how to reinstall Logic if thats the route you choose to go:
[quote]Normally, you shouldn't have to reinstall Logic Pro, but if a need arises (such as if you're troubleshooting), you can reinstall the software using these steps.
Click the Finder icon in the Dock.
From the Go menu, choose Go to Folder.
In the resulting dialog, type /Library/Receipts in the field.
From the resulting window, drag the following items to the Trash (depending on which versions and updates you've installed, some of these files may not be present):
Logic Pro Sound Library.pkg
Logic Pro Bonus Sound Library.pkg
Reinstall Logic from the original installation disc.
Use Software Update to get the latest Logic update.[/quote]
I'm still struggling to figure out if its a hardware or software issue.
Do you have another Mac? Or a friend with a Mac that you can use? Try open the same Logic projects on there and see if the same issues happening. If so, then you know its a Logic project issue, and not a Mac issue.
Sorry, about all the questions, but one way or another we'll get to the bottom of this.