When you want to reuse a CD-RW disc that has files "burnt" on it already, you need to erase that content first. Erasing a rewritable CD using Windows Media Player is an easy process. Microsoft advises users to ensure that the CD is a rewritable CD, also known as a CD-RW, since a CD-R disc cannot be altered.
Open Windows Media Player. Select the "Library" tab from the top navigation bar
Insert the CD-RW disc you want to erase. The contents of the disc will appear on the screen.
Find the CD-RW icon and the name of the CD-RW on the left pane. Left-click on it to ensure this is the disc you want to erase with Windows Media Player. This will pop up what drive it is in and the name of the CD-RW.
Put your mouse over the CD-RW name and right-click. Select "Erase Disc." A pop-up window will appear confirming you want to erase the disc. Click on the "Yes" button. This will erase a rewritable CD using Windows Media Player.