QuickBooks Point of Sale & QuickBooks Enterprise

Many years ago when I begin using QuickBooks, after the man that was helping me installed my QuickBooks and set up my two small business with there company names and there checking accounts in QuickBooks.  Then he showed me how to access them each and / or how to add a new company and its name in the future if I ever needed that.   As it turned out over the years I did need to do that and I have added four different companies and there related checking accounts that I needed to manage for my now deceased husbands business activities and never had any problems adding them or using them after they were added.
 
From what every that man did, whom originally installed and set up my QuickBooks companies.  When I clicked on the QuickBooks icon, that's on my desk top screen, I would first get a BOX that had a heading NO COMPANY OPEN.  Then below that were the two company names listed that I had at that time, and then over the years as I added new companies, that names list has grown.   Out of that names list, I click on the company that I want to work-in, and then I am ask to enter my password, and then it opens to that company that I had clicked on.
When I am done working in that company name and I want to go work in another company name, I go up to: file at the top of the screen and click file and then drop and click on close company, and my screen goes back to that box where I can open another company to work in or I can go up to top of the screen and X out all together and return to my desk top screen and other icon's..
 
So how was I able to add those new companies?   Below the list of company names is a sentence that says:   location: C:\Documents and Settings\ Owner\ My Documents\Quick Books\.  Then below that sentence are three small boxes within the large box.   The names in each box are:  Create a new Company     Open or Restore an Existing Company     Open a Sample File   & this one is followed by a drop down arrow.  I have never used the second two boxes only the first one, create a new company.  That  is how I created the other company names and information years later when I married.  After I filled out the requested information on the company, each company name as it was established appeared in that box and I never had trouble switching between company names.
 
So what is my problem?   I have son's whom have there own businesses and I am going to be using there new QB  Pro 2010  to keep there company checking, etc. for them.
Here to like myself there is the need to set up more then one company name and information so I can work in both of them and switch between them as needed.
 
My son installed the QuickBooks  Pro 2010 onto the lap top, and then I clicked onto the QuickBooks icon on the desk top and set up the company name and then clicked finish and left for a few days.  When I returned to the desk top and clicked on the QuickBooks icon and expected to see the box as I have on my computer so that I could then create the additional company name and information there was a problem.   What was that.  When I clicked on the QuickBooks icon it only ask for my password and then takes me into the company that was first set up. There is no box or anywhere for me to add another company name or way to switch between more then one company name.
 
How do I get that box with those options to show up in my sons lap top / QuickBooks Program, as it is in my computer and its QuickBooks program? So that I can set up both of my sons company names and information in there QuickBooks program and switch between the to of them as needed.  I am sure you can help me and I am every so grateful that your here for me, your my pearl in the hay stack.