Let me begin by stating that I have a Dell Dimension 4300, Pentium IV, 1.7 GHz, 512KB RAM, and an 80 Gig hard drive.  Never had a problem with my computer (purchased it in 01/2002) until now.

EXAMPLE #1 - Backing Up/Copying to a Previously Used CD-RW Disc 
On 8/14/04, I backed up one of my files to a CD-RW disc in the CD-RW (E:) drive without any problems.  Today, when I tried to backup another file I get the following message:

"Cannot copy (file name here): Files on this CD are read-only. You can still copy new files to this writable CD, which will replace files already on the disc." 

It should be further stated, that the ability to delete on the writable CD is no longer available either.

EXAMPLE #2 - Backing Up/Copying to a New CD-R Disc
The first observation that something was awry, is that in Windows Explorer under My Computer, the writeable drive which normally reads CD-RW Drive (E:) changes to CD Drive (E:) upon inserting a blank CD-R disc into the drive.  Likewise when removing the CD from the drive, CD-RW Drive (E:) name reappears.

I also discovered that when trying to back up/copy a file to any CD-R or CD-RW in the drive, the message:

"E:\ is not accessible.  Incorrect function."

pops up.  The bottom line, I cannot back up/copy any files to the CD-RW (E:) writable drive.

Upon Further Review:
I know computers enough, that I did some additional investigating.  Right-clicking on the CD-RW Drive (E:) when it is visible and selecting Properties, then the Hardware tab, it states:

HL-DT-ST CD-RW GCE-8160B - DVD/CD ROM Drives
Device Properties:  (Standard CD-ROM drives)
Location: 1 (1)
Device Status:  This device is working properly

Anyone have any suggestions for me?  This PC has worked flawlessly for 2-1/2 years until today.  Thanks for taking a moment to read about my dilemma.

Brett