Cant use my brand new logitech webcam, Plz Help me...

Hi to all experts here,

I bought a Logitech Quickcam Communicate STX webcam last week, juz installed the drivers from the cd, after that, the application asked me to plug in my cam, after i plug in the cam, the application could'nt detect the cam , so i reboot the pc wit the cam plugged in, i went to "My Computer" and check it out whether my cam is there or not, i saw my webcam appearing and gone every 2 seconds, like pluggin in and out!!!, i can see the device at "My Computer" every 2 seconds! I dont know how to solve this problem, first installed the drivers and the softwares. and i uninstalled all and tried installing only the drivers, still no use

Went to "Device Manager", still refreshes every 2 seconds.

I tested the webcam on both of my usb ports, still no use, my usb ports are also working fine cuz i use my mp3 player to copy my music.

And one more thing, the webcam worked perfectly fine at the shop where i purchased !!!

The cam supports USB 1.1 and USB 2.0

Here is my pc config:

PIII 1GHz
40GB HDD
128MB SDRAM(PC-133)
In-built graphics
D-Link Ethernet card.
USB 1.1

OS : Win XP Home SP2 (Updated everyweek)

Please help me guys. I'm very frustrated bcuz of this problem...

Thank u all
Wish u all a Merry X'Mas and a happy new year