Windows 7: Trouble installing Windows 7

Something weird happened, when the HDD was being cleaned (with the clean all command) this message popped up: 'DiskPart has encountered an error: The device is not connected. See the System Event Log for more information.'
When I tried to clean it again it didn't show up when I listed the disks again, and I'm fairly sure nothing happened inside the box.
I'll reboot and try and do it again.

A simple reboot didn't make it appear again in diskpart (I also checked the BIOS and nothing), so I cut the power for a few seconds and there it was again, but when I attemped a second 'clean all' a different error showed up in the middle of it: 'DiskPart has encountered an error: The system cannot find the file specified. See the System Event Log for more information'. Do you make sense of it?
Anyway, I'm going to keep at it and see what happens.
Edit: as the first time, the HDD disconnected.

Since clean all didn't work (after 3 attemps) I just did a 'clean' and then created the 100Gb partition and tried to install on it, but I arrived at my original problem: installation stuck for a couple of minutes at 0% followed by the error: 'Setup was unable to create a new system partition'.
I am going through the links you provided, so for now I don't need any more help, but if get stuck anywhere else I'll let you know.

Looks to be a bad ISO or bad HD.

Check the hard drive with the manufacturer's diagnostic tools.
Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
HD Diagnostic

I keep getting the 0x80070057 error every time I try to install, even after trying the suggestions from this link Common Installation Problems and Their Solutions
One thing that I noticed is that the HDD 'disappears' when I do actions such as formatting, cleaning the whole disk, and installing Windows, so I guess either the HDD is at fault, or its interaction with the computer.

The diagnostic is running right now, but I can already say that there's something wrong with the HDD, since there were several errors before the read surface scan, and in this very scan, which is at the moment at 0.002%, has had at least a thousand errors. Does this mean that the hard drive itself is damaged, or that it's badly connected?
Edit: I stopped the full surface scan at 0.004% and restarted the diagnostic (ommiting the surface scan) and when it finished it told me that there were problems with my HDD and that I should contact with my dealer, so that's what I'm going to do next.