Your floppy drive / floppy may be faulty. Try to run it from CD.
The following from click here:
"Run from CD
Memtest86+ is directly executable by any modern x86 compatible machine, by writing the iso to a CD one can boot from the CD to run memtest.
Simply download the appropriate package, the Download - Pre-Compiled Bootable ISO (.gz) for Linux users and the Pre-Compiled Bootable ISO (.zip) for Windows users.
For Windows, unzip the package into a directory like C:\memtest. You will now see a file called memtest86+-1.xx.iso in this directory. You will need to burn this file to a CD with a CD recording program. Do note however that you should not make a regular data CD on which you for instance write your text documents and holiday photographs. Instead the iso file is a so called image of a CD, it is a direct copy of a CD. Your CD recording program will most likely have a feature called burn image or something to that effect which you should use to burn the CD.
When the burning completed your drive will most likely have ejected the CD and you should have a bootable memtest86+ CD. To run the test directly reinsert the CD and reboot your machine.
Your machine should now boot from the CD, display the word Loading folowed by a series of periods and then show a screen much like the screenshots on the memtest86+ web page. The test is automatically started.
If your machine simply boots back into Windows/Linux you will most likely have to configure your BIOS to attempt to boot from CD-ROM drive on startup, refer to your computer's/mainboard's manual how to do this.
When you are done testing simply remove the CD and reset your computer, if ever you want to execure the test again simply reinsert the CD and reboot/start your computer."