Windows 7: Virus Hides and will Not Show Files Folders

Hello. Newbie Here. I have Win 7. I just purchased this Dell Laptop with preloaded software and apparently free viruses. I've used the following to disinfect the laptop. Malwarebytes, Sophos, TDSSKiller, Spybot S&D, ComboFix and running Avast Antivirus. I think this computer is virus free, but I don't know for sure.

I think the virus did some damage to my registry. When I attempt to Show Hidden Folders by clicking the radio button, then click appy,....Ok, it doesn't work. When I open the Folder Options box again, it shows the files are HIDDEN. It automatically reverts back to DONT SHOW. I've tried to use Unhide.exe, but a pop up applet says "There was a problem retrieving a necessary environment variable. Unhide has Terminated"!

Inside the Unhide.exe CMD box it says "appdata doesn't exist! Unhide Terminated! I would love to get this resolved. Let me know what you need. Thanks in advance.

Have you went through all of this? Are you the administrator?
File and Folder - Hide or Unhide

I am not sure what you mean by a DELL Laptop with preloaded software.

Who preloaded the software and what software?

Did you purchase a new DELL laptop with factory installed Windows or did you buy it from any other source (usually with no scruples) that installed these software?

Is it still running the OEM installed Windows?

Does your DELL laptop still have a in-tact recovery partition from which you can restore to the factory image?

If someone had reinstalled Windows from some other media, did you get a valid product key that will be necessary if you are required to do a clean install?

Atleast I will not give any suggestion for fixing your problem unless there are clear-cut answers to these queries - the reason being if something goes haywire while trying to fix the problem, you should be in a position to do a reinstall/clean install. I am not sure whether you are in a position to.

@ Jumanji. I purchased a used laptop with Win 7, Office and other programs. I haven't installed anything except anti-virus type programs. I've already done a restore, but the date was just about 10 days ago. Don't have a valid product key. I think this system came with Vista and the last owner put Win 7 on it. Sorry, but don't have history on this other that it was a student laptop. FYI, I'm using the computer right now and it seems to work fine...just a few small things, like the Show All radio button automatically reverts back to Don't Show, when I right click on the desktop, there is no context menu under NEW and I just created a Standard user but it logs me off of that acct immediately after logging on. Don't know if you can help, but thanks for responding.

@Layback Bear. Yes, I'm familiar with those other options, but would like to fix the Show All Files problem. Yes, I'm logged on as Administrator. Thanks for responding.

You say you don't have a valid COA key. That is the first thing you must have to make your system legal and work correctly. Is their/there a COA sticker on the computer? On the bottom or in the battery compartment. It will tell you what operating system your laptop came with.You will also need a key for the Windows Office program to make it legal.
What operating system does the COA key indicate. Please don't post the number here.

I just looked and unfortunately the sticker is not legible. I guess that's what you get when you buy used from ebay. Thanks.

My research indicates your laptop came with Windows XP. This might be of some help.
Windows Genuine and Activation Issue Posting Instructions
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Once the log is posted their/there are people here that will be able to read them and help you.

Oh. Thank You! If you don't mind me asking, how did you find out this came with XP? My other laptop came with XP and I love it. It seems so much more stable than Win 7.

Dell Latitude D830 Specs (Core 2 Duo 1.8GHz, 512MB RAM, 60GB HDD, Windows XP Home) - Laptops - CNET Reviews

GREAT Info!! How do I close this post? It hasn't been solved, so I don't want to mark it as "Solved". I've seen too many other posts marked as solved when they really weren't. Thanks.