My Lenovo laptop with debian6 is not detecting usb drives. please give me your valuable suggestion...

Have you enable usb modes in the bios?

do you mean as in "booting from usb" or in "automounting usb"?
if the first, eddy1's suggestion. if the 2nd, post output of "lsusb" with memory stick plugged in.
anyhow, Debian 6.0 ("squeeze") — obsolete stable release.

Try booting into bios & check the usb settings it is possible that they are disabled.

yes, i have enables usb modes in the bios.

Hi lojo,

Does your system see the USB device?

The system typically auto-detects it similar to what is shown here w/the blkid command:

(Note: on Debian you may not need to use sudo, adjust as required. Commands are shown in blue, output is shown in green)

From a terminal session:
sudo blkid /dev/sdb1
/dev/sdb1: UUID="3722-5DEB" TYPE="vfat"

If it is there it may/should also show under:
sudo fdisk –l with or without a mount point.

If it is not mounted, assuming it is /dev/sdb1, mount using this with the proper filesystem type:
sudo mount -t vfat /dev/sdb1 /mnt/usb (Note you may need to mkdir the /usb, adjust the sd*# as appropriate)

Again, sudo or su to root as required.

If that does not fix it it might be helpful if you post the output of the
blkid and fdisk commands.

Hope that helps and all the best,
Tim

Have you enabled the LTS mode in Debian6? Instructions are found here. If you don't want to use LTS then it would be a good idea to update your Debian to Debian7.
jdk