The solution depends on how your BIOS menus are organised, but yours should have a "Boot" menu on the top bar, you should go there and see the boot order. Almost certainly, under the boot order, there are a few other items, one of which should be something like "Hard drives". Go there, and select your WD200 (or put it at the top of the list, if more items are listed). Then press esc to go back to the main menu and rearrange your boot order. Finally, press F10, save the changes and let the computer restart.
Let me know if this works.

First, check the boot drives to make sure that the computer is not trying to boot from a different drive to the one that contains Windows.
Check that there are no CDs or DVDs 3 1/2 inch floppy discs
in the CD/DVD,3.1/2 floppydrives.
Test all leads that attach to your hard drive including electrical extensions,IDE,SATA
the leads from your ((motherboard to your hard drive)) make sure they have a secure connection and are not faulty or just replace them there probably old and faulty
make sure all leads that are attached to your drives dvd\cd 3 1/2 inch floppy have secure connections and are not faulty if this does not fix the problem it might be a registry problem
Close all open programs

Click on Start, Run, and type regedit and press Enter
Click on the plus signs (+) next to the following folders

HKEY_LOCAL_MACHINE

SYSTEM

CurrentControlSet

Control

Class

{4D36E965-E325-11CE-BFC1-08002BE10318}

This folder is the DVD/CD-ROM Drive Class Description in the registry. Look for any of the following names in the right hand column.

Upper Filters

Lower Filters

Upper Filters.bak

Lower Filters.bak
If any of the above keys shown in step 4 are listed, right-click on them and choose Delete

After deleting the keys, close the registry editor
Reboot your computer
Open My Computer and check to see if your CD or DVD drives have returned. You may also want to open Device Manager and verify that the yellow exclamation and error code on the CD or DVD drive is gone.





hope this helps