Can't change Computer name

Hi guy this is my first post here! I have very unusual problem whit my computer name.
Last time I reinstall the computer, I left it to stand in the middle installation( I was on a party :)).When I get back on my screen was a dialog box where I need to put the serial number. BUT before that I should enter my username right? But that never happened.
Windows put this username for me: "dfgfghjfguiyabfdytuy"
I tried everything but it just won't work.I changed computer name to ''Workstation'' but when I try to, for example, extract some file to my desktop in Winrar (and in every other program) it says : ''C:\Users\dfgfghjfguiyabfdytuy\Desktop'' for the destination folder.
So please if someone knows the solution to my problem I would be very grateful to him.(it won't work when I right click in my computer, go to properties and under tab ''computer name'' change settings). I will post screen shot to help you!
Thanks!!!!!!!

It sounds like somebody typed in that gibberish for your user name when you weren't looking. Even if you go into user accounts and change it, ''C:\Users\dfgfghjfguiyabfdytuy\ will never change. Your user name will change everywhere else its displayed, like the welcome screen, but your user folder name won't. To get around that you would have to create a new user, transfer all your documents and pictures, etc to the new user account, and then delete the old user account.

It seams that I changed the name correctly and I think that alphanumeric answer is the right one.Thanks you guy for your help!!!