continued...
As your computer starts up you have the opportunity to go into your BIOS and check it is ok, or make changes.
Watch carefully as your computer starts up (before Windows starts to load) and it will say something like "Press Delete key to enter BIOS" (it may not be the Delete key on your computer).
You MUST press this key BEFORE Windows starts to load or it is too late. If you miss it, then shut down the PC and try again.
The main BIOS window wll look something like this:
http://www.blog.tycotec.com/wp-content/uploads /2008/04/bios.gif
Once you are in the BIOS search round for the place where your devices are listed (hard disk etc). For the hard disk set it to AUTO and it should hunt round and find your hard disk.
If it finds the disk then chose the option like "Save changes and exit" and then restart your computer.
Hopefully when it restarts then Windows will restart.