Well, there's no doubt then that the problem is not related to your wifi signal.
In order to isolate and confirm that the problem is undoubtedly your internal wifi (versus router or other issue), the only thing that I can think to do now is for you to obtain (buy) a USB wifi, install it (drivers) and see if it stays connected. You could then return the USB wifi to the retail store after the test.
If you do this, get fresh drivers online from the USB-wifi manufacturer online as the drivers that come burned on a CD are usually old/out-dated.
What router do you have? I don't mean the brand or model, but where did you get it from? Did you buy it or do you lease it/get it free from your cable company or FIOS or other Internet provider?
How old is your laptop? (Sorry if I asked this already)
Regards. . .
jcgriff2