Hey this is to ask you that my flash disk can not be formatted, so would you help me if you encounter this problem before.

Some flash disks have a locking mechanism that prevents accidental erasure. If you move it to the other position perhaps your issue would be solved. Also, when you encounter issues with a flash drive, it's a good idea to try more than one PC connector as the ones in back are usually of a higher power (directly off the motherboard) than the ones on the front of the case. Flash chips are not meant to last forever, and cheap Chinese ones have been known to fail early.

I had the same issue with a Transend flash disk. I just downloaded a recovery tool from their website.
Check the manufacturer's website.

These $#%&@ autorun viruses could also be a cause.