Hello Jean,
I would first start off by identifying why the dell technician was attempting to move your data, it sounds like you have a bigger issue going on like running out of free space.
Now you will want to identify how many physical Hard Disks are inside your computer. you can do this using a program from the web that will also let you know if your Hard Drive is throwing any errors. Visit hdtune.com and download the free trial, once installed you can launch the program to view the status of your Hard Drives. If you click the dropdown menu and find a second device, then now we know there are indeed twos Disk Drives.
Your best bet is to use an external Hard Drive and copy all of your data from the D:\ over to it along with data from c:\users\
Then follow our guide on Komando.com to perform a clean Windows installation, once done with that you can restore your data from your external Hard Disk Drive and start installing your applications.
Let me know if you have questions.