U mean turn on and off right?

That's generally what restart tends to mean, yes.

Jeez man. Just restart it. It will boot back up again.

No amount of restarting fixed my problem. But hey, it might not be the same thing.

You could always call customer support

There are several scenarios that could've caused Windows to not be able to find the file that its looking for, "Hsdev.exe".

1) You've got a faulty connection. In that case you just open the case up and plug the hard-drive in, simple as that.
2) The file has been moved. Again, this can be fixed, no hassle. Not sure how we'd fix it yet, but we'll get to that bridge when we cross it.
3) The Hard Drive has been corrupted at some point, rendering "Hsdev.exe" unreadable. Simple solution to fix this would be a Disk Check.

Basically, try running a Disk Check first. To do so:
1. Go to "My Computer".
2. Right click C:\ Drive and hit "Properties".
3. Go to "Tools", and select "Error checking", "Disk Checking", something along those lines.
4. Tick both "Automatically fix file system errors" and "Attempt to fix bad sectors".
5. Start running it. It'll tell you it can't check the volume while it's in use; let it schedule a disk check and then reboot.
6. You'll be presented with a black screen & white text upon bootup. This is what we want; let it check the disk. The time it takes depends on your hard drive, but my 300GB Hard Drive generally takes 90 minutes.

If you still get the error after disk checking, post back here.

Also, a restart won't fix it, Geno :V

You've neglected to give us some crucial information that would help us help you.

1. What are your system specs? Like OS, CPU, that stuff might help.
2. More importantly, what are you trying to do? Are you trying to burn something on a disk? Are you trying to bake bread? What?
3. Also important, what were you doing to try to do that? Like if you were burning something onto a disk, but didn't have a blank CD/DVD in the drive, "Disk not found" would make a lot of sense.
4. What scenario did you get your error message?

etc etc etc

EDIT: I misread OP.

Use control alt delete, if you're running Windows, and go to the Processes tab.
Look through the list of processes running and google ones that you don't know. Look up what they do, etc.
Make a list of potential programs that could be trying to access your disk drive.

It's possible that you have a program running in the background that you were using previously but didn't close properly that is now trying to access your disk drive.

Wow... It worked

HUZZAH!

That's good news.

Lol whaaaaaaat.
Ah well, good to know it's working.