My phone no longer syncs with my computer

I own a mac. For the last few months I've had no problem syncing the phone with the computer, just plug it in, hit "mount" and it shows up as an external drive. Now all of a sudden it's decided not to do that anymore, and instead when I plug it in it shows up as a CD entitled "Verizon_mobile." I cannot access the drive, and it says "The disk you inserted was not readable by this computer." This change literally happened overnight. What happened here?

For a Mac:  this is a bit of a process, but full proof.

Plug your phone into your Mac via USB.  Go to Settings>Applications>Development and for the moment select "Stay Awake."  This will just prevent your phone from sleeping through the process. (Just be sure to uncheck that when you are done!  Dead batteries suck) 

After you plug in the phone and the USB message comes across the status bar, swipe down on the screen and select "USB Connected -Select to copy files to/from your computer."

Select "Mount" when the blue USB connected message pops up.

Wait a few minutes until you get the "Disk you inserted was not readable" error on your Mac.
Select "Ignore".

At this point, just to be sure, open "Disk Utility" on your Mac, you should see an entry for "Samsung SCH -I500. Select it and then hit "Info". Look at the Disk Identifier, it should say disk1 or some other number. Remember the disk #.

Open Terminal (in utilities).

If it is disk1 just type "gpt show /dev/disk1" (without quotes) in Terminal. If it is disk2 or another number just change the 1 to whatever number yours happens to be.

When you have that copied in Terminal, look back at your phone and "Turn off USB Storage" select "Turn off" on the blue message that pops up.

Wait a few seconds and the "USB connected - select to copy files" message comes back on your phone.

Select it and select "mount" again. Once the status bar cycles through past the USB connection image, bring up your Terminal and hit "enter" to run the command.

You should get something like this,
start size index contents
0 1 MBR
1 128
129 30904191 1 MBR part 12

You will see your phone (looking like an external hard drive), show up on your desktop.  That is your SD card.  You can drag and drop just like you used to.  Unmounting is still the same as before the glitch... er... update!!

Thanks for posting this question, it is exactly what happened with my phone/computer a month ago. And thanks fascinator296 for the solution! I registered for the site just to tell you how grateful I am 

My phone finally works. I have spent hours on this. Thank you soooooooooooooo much!!!! <3