Ok, I'm making progress. There is some Mac Help on this subject. Search Startup and you will find the "You need to restart your computer" message, and it says,
"You need to restart your computer" message appears
This message indicates that an error occurred in the core of the operating system, which is referred to as a kernel panic. A kernel panic can be caused by damaged or incompatible software or, in rare cases, by damaged or incompatible hardware. The most likely cause of the problem is that a system file or folder has been moved, replaced, or damaged.
If you know that you have moved or renamed a Mac OS X system file or folder, then you must reinstall Mac OS X. (It won't work to just replace the specific item.) If you are not aware of any changes to Mac OS X system files or folders, try the following procedures.
To reselect your Mac OS X startup volume:
Restart your computer. Most often the panic is an isolated event that requires no further action.
Restart your computer while holding down the X key. This may force the computer to start up using your Mac OS X system. If it does, release the X key, then open System Preferences and click Startup Disk. Make sure your Mac OS X system is selected.
If you are unable to start up using the X key, restart your computer and immediately press and hold the Option key. Release the Option key when icons start to appear in the center of the screen. Select the Mac OS X system disk, then click the forward arrow to continue starting up.
If the above attempts to reselect your Mac OS X startup volume are unsuccessful, try resetting PRAM. Shut down your computer, then turn on the computer and immediately press and hold Command-Option-P-R until you hear the startup sound for the second time. Open System Preferences, click Startup Disk, and select your Mac OS X volume.
Note: Resetting PRAM may change some system settings and preferences. Use System Preferences to restore your settings.
Open this for me
"Mac OS X: "Broken folder" icon, prohibitory sign, or kernel panic when computer starts" webpage
I restarted using the "X" key, and that did not help. If I start up in safe mode, by holding down the shift key, I do not get the message. I started up on my backup drive on a seperate hard drive, and so far it has not frozen. I guess I will try resetting the PRAM next. It looks like this started happening when I upgraded to Safari 3.1.1, as my backup is v3.1 Not sure if that is the cause though...
Will keep in touch.
Bill