Ice cold; Thank you for your suggestion, I have taken all these step before, the problem is:
1) I have three hard drives with lots of partition which they have taken the entire A-Z drive letter except for letter "B".
2) I have two USB flash drives from two different brand one 256 MB capacity which Manage Disk has assigned letter "B" to it, therefore is being recognized and is accessible as "Drive B". The other flash drive is 512 MB and can not be recognized because there is no more letters is available to be assigned to it.
3) The problem is when I disconnect the 256 MB flash drive and connect the other drive (512 MB) to the computer the Windows XP fail to assign the same letter "B" which is unused to the 512 MB drive. Therefore is not being recognized and not accessible