Windows 7 forum: Just bought a used Sony Viao and want to be sure it's clean!

...no, forgot that important note: I do not have the restore disc.

I, unfortunately, do not have the restore disc nor any documentation to which to refer, so your advise is greatly appreciated. Will the system restore and adding and deleting of admin users do the trick?

What I noted about user accounts has been around for many years. I didn't add any new tricks or twists to the process so I have to make an assumption this is your first PC.

Given that, you must backup the entire machine before you do any work.
Bob

Yes, It's my first used computer. How do I do a back up?

I suggest you get away from the Windows backup program and get yourself a good commercial backup program. I've seen forums fraught with problem reports for the Windows one. I know I was very unimpressed when I tried it. Three I'm familiar with and like are Norton Ghost (which I've been using for 8 years without the 1st problem), Easeus Todo Backup Free, which you can download from http://www.todo-backup.com/products/home/free-backup-software.htm and Memeo which has a 30 day free trial and you can buy it for $29.99 - you can download it from http://memeo.com . You can get Ghost for next to nothing (like I did) if you watch the sales.
The March 2012 issue of PC World was very high on the FREE program from Easeus and so is CNET. In my experience with a variety of configurations I have to say I'm very impressed. Like Ghost it will back up to a networked drive, and it will create a boot CD for when your PC won't boot. See CNET's review of it at
http://download.cnet.com/Easeus-Todo-Backup-Free/3000-2242_4-10964460.html?tag=mncol;1#editorsreview .
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CNET has a lot of backup program reviews at
http://download.cnet.com/windows/backup-software/?tag=contentBody;sideBar .

Some of these are free (last time I checked there were over 300), some have free trials (over 1000), and some are purchase only (over 200).
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External hard drives are best for backup. You can get a 500 GB one for around $60 and a 1 TB one for around $70. You can also buy a 32 GB flash drive for under $15. It's the best insurance you can ever buy!

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I hope this helps. Good luck