Best Buy Stores (National Chain) Thieves, liars and just plain dishonest Burleson, Texas

Let's see you had them remove "a" Virus.  Well first Viruses are like Cockroaches or Ants.  If you see one there are hundreds you don't see.  Second, if you had to have them remove one that means you didn't have any Anti-Virus software installed, or if it was installed you didn't have it running. 

As for the "I never go into chat rooms, and don't have children"..please.  Off the top of my head I can think of at several ways to get a virus or worm on a computer and none involve children or chat rooms.  Such as going to an infected web site, opening a document you receive through e-mail, not keeping up with updates to Windows(assuming you are on Windows).  Given time I could probably come up with several more as well.  Quite frankly having kids may have saved you from this, because there are a lot of kids that have more computer knowledge than some adults.

Also, yes a hard drive can be "broken" and still be able to get data off of it.

The only claim that MAY be valid is if you say they did not return a cable you gave them.

Get a firewall, get anti virus, get a spyware detection, keep all software and drivers up-to-date.  I recconmend NOD32, F-secure, or AVG,  When you are not using your computer turn it off. Does not hurt to unplug it either.

Next read up on computer maitence...

Never open an email or attachment unless you know exactly who it is writing you or what you are opening, most providers will scan it for you as well, you should do the same.