|There are many types of disk drives. I assumed you meant hard disk drive, not optical disk drive.|
What OS came on the mini?
You should be able to perform a restore to factory settings of the hidden partition on the hard drive.
Why waste a WinXP home license?
Now, to explain why you are getting the message you are seeing. The mini is most likely NOT booting to the flash drive. Enter the BIOS (setup) screens and change the boot order. As I stated, unless you wiped the entire drive ( a big mistake) you should be able to restore the mini back to the way it was bought.