Cannot Bood from Disc

I know you guys get a lot of this and I've been through several related threads but have been unable to solve my problem thus far.

I am trying to wipe the hard drive on an old Toshiba laptop currently running Windows XP. To do this, I put the disc image file of DBAN on a CD and started the computer. Here is what happened:

1. I hit F12 to enter the boot menu.
2. I selected "CD-ROM/DVD Drive" which was the second choice in the menu after "Hard Drive".
3. A black screen with a cursor appeared briefly, then Windows started as usual.

So, I started over:
1. I hit F12 to enter the boot menu.
2. I selected "<Enter Setup>"
3. I set the "CD-ROM/DVD Drive" to #1 in the boot menu tab.
4. I hit F10 to save and exit.
5. Windows loaded as usual.
6. I restarted the computer.
7. Windows loaded as usual.

So, I started over:
1. I hit F12 to enter the boot menu. "CD-ROM/DVD Drive" is the first option.
2. I select "CD-ROM/DVD Drive".
3. A black screen with a cursor appeared briefly, then Windows started as usual.

So, I started over:
1. I hit F12 to enter the boot menu. "CD-ROM/DVD Drive" is the first option.
2. I select "CD-ROM/DVD Drive".
3. I hit F12 again as per a recommendation from a thread detailing a similar issue.
4. A black screen with a cursor appeared briefly.
5. The error "PXE-E61 Media Test Failure Check Cable" appeared twice (I believe it made two attempts).
6. Windows loaded as usual.

I tried removing the disc and reinserting the disc and trying some of these again, but I got the same results.

What can I try now?