when you click on the defrag and the list shows 2 drives/disks ?? {can be called by either name = same thing}

I think the {D} in your case is your recovery and back up files - I hope you didn't delete those??? those are your safety net if you don't have a CD for reinstalling.
{but that drive shouldn't really be showing to you or alan - it should be set as hidden so nobody deletes it by accident...

Did you ever make those recovery disks it wanted you to make last month?

If the D drive is what was deleted go to your recycle bin and restore all that info.

only clean and defrag the C drive unless you know you have more than 1 actual hard drive in your machine.
some people add many but since yours is factory it should only have 1 hard drive installed.

What your recovery files are on is a partition of your C drive and it is called the D drive.
In other words your HD is sectioned for safety and the recover files are in that section.