I am sure that all my ports are working, i tried to use other flash disk to check if the port is working. It's an 8Gb pqi flash disk. Its working last day but now even the device manager cannot detect it. Please help.
If you removed it after writing to it without doing the "safely remove" operation, then it may be scrambled to the point that the OS cannot see it to mount it. IE, if the MBR of the disc (1st sector) is not recognizable as an MBR, then you may be SOL. With Linux you could fix that easily, but I'm not so sure with Windoze.
Boot linux (either an installed copy or a live cd/dvd/usb drive), go to the command line and look at the drives detected in /dev, such as /dev/sda, /dev/sdb, etc. Do this before you attach the flash drive. Then attach the flash drive and see what its new drive specifier is, such as /dev/sdx. You can then run "fdisk /dev/sdx" to see or change the partition table, or even write a new boot loader (mbr) to the device.