My WD Essential hardisk doesnt work only with my pc

While you say it doesn't work.... what exactly message coming out...?

You mean it cannot detect by the USB ? or what error coming out..

Does anything work in your USB ports?

You have a USB hardware failure, or Windows software issue.

You'll need to do basic troubleshooting.

If you aren't good at troubleshooting, try this:

1) unplug your PC and open up the case
2) unconnect your WINDOWS hard drive (to prevent messing it up)
3) connect a SPARE hard drive
4) Install Windows to the spare hard drive
5) Install the motherboard's main chipset drivers

*at this point USB should work fine. If it works, you'll need to either try reinstalling the main chipset driver for your motherboard, other software fixes, or simply reinstall Windows (after saving important data).

UBUNTU LINUX:
You can also simply run WUBI to download, and install a copy of Ubuntu. If your hard drive works under Ubuntu then your issue is a Windows software problem.

Ubuntu (installed with WUBI) can easily be removed from add/remove in Windows. To enter Ubuntu you reboot the computer and choose Ubuntu from the boot manager.

It's actually pretty easy.