Hi, We would need to know some things:
Does this drive function and does it contain files, if so, what are they, any important files like drivers, backed up system, your data, etc...
Did you start with only one drive, C:, the tech may have just renamed your D: drive?? Computers such as Compaqs come with a Restore partition that you need. If yours is not that type of name brand machine, then you are a bit better off...
Do you have one or more actual hard drives in the computer?
That is, has anyone installed an added in extra hard disk?
What software has the drive been created with, just a partition from the Windows component fdisk, or software like Partition Magic, Ghost, etc? Windows has software that creates full or partial backup....called logically enough, Microsoft Backup, stored in a separate partition it creates when you enable a backup....did the tech do this?
Storing data on the same hard disk is only one way to "back things up"- but, if total disk failure occurs, where are you?
Always best to use removable storage if possible, such as to CDs or another hard drive or in case of very important stuff, both.
If this is a created partiton, you can certainly delete it using fdisk, a built in tool, but will lose ALL information on that partition....if you have Partiton Magic, it can be merged I am pretty sure with Drive C: and there may be other softwares that can do this. You must know what is on that partition FIRST though....if you are going to be deleting the partition, you will have to move anything you need. Programs on that drive willl have to be reinstalled!