Safari and Entourage suddenly won't connect, or stay connected (dial-up)

Question

Help! (Please note that this is a question about a MacBook; ignore "Powerbook G4" signature).
The Safari and Entourage applications on my new MacBook, which is on an Apple USB external dial-up modem (NOT wireless or Ethernet), have suddenly stopped connecting. Manifestations:
(1) Safari: When Safari is opened, it connects normally via dial-up to the start page (Google), but then either won't connect to the next website or goes to a new website, then disconnects after a minute or two. The error message then appears: "You are not connected to the Internet. Safari can't open the page [website address] because your computer isn't connected."
(2) Entourage: After this problem recurred several times, I decided to test Entourage, which had been working fine. I connected manually to the Internet, and with the connection holding, I tried to send a test message to myself. I then got the error message, "Your Mac OS Network Preferences are not configured to allow automatic connections" (they were, and anyway, the computer was already connected). The computer then disconnected and I got the message "The computer has disconnected because the other side is not responding."
I've tried the following, without success: (1) Restarting. (2) Resetting Safari. (3) When neither helped, I double-checked my network configurations, as well as my account settings in Entourage, and they all seemed okay. However, each time I typed the correct password into the network configurations box, it added about 8 additional dots as soon as I checked "Apply." (I've been told that this is a security feature, but it hasn't happened in the past.)
I then checked the settings using the Apple Network Diagnostics program that Safari offers. ND verified that the modem, modem settings, and ISP settings were okay, but that "Network Settings failed," "Internet failed," and "Server failed." Since the network settings looked right, I don't know what, if anything, this means, or whether the problem comes from something else.
Thanks for any suggestions anyone has.

Answer 1

Mandita 3 and Virtual Canary: Sorry it's taken me so long to get back to you. If you're still tuning in, in my case the problem of random disconnects on the USB external modem seems to have been resolved by simply switching USB ports on the MacBook.
I talked yesterday to an AppleCare "product specialist"--ie, a level 2 techie--whom I had requested to take me through an Archive and Install of OS 10.4.6 to downgrade from the 10.4.7 upgrade I had done, which I thought was causing the problem because the kernel panics (recorded in my computer's log) began happening right after that.
He suggested that we first try the simple expedient of switching to the other port--he said that he had had this problem several times on his own computer with other USB devices, and that had done the trick; if it didn't work, we could still do the Archive and Install, but he said that "Some USB devices just turn out to be incompatible with one or the other port; it's just quirky."
I've been testing the machine for a couple of hours and the switch seems to have taken care of the problem (to double-check, I went back to the first port once and the random disconnects after 2-5 minutes began happening again).
I've only been testing the machine for a short time, so I can't say for sure that this works. Also, even if it does work, I'm going to call my authorized repair place and ask if the "defective" port can be repaired or replaced--it was working fine for the first 6 weeks that I had the machine, so presumably the one that still works fine could develop an allergy to the external modem, too.
Hope this information is of use to you.