wireless connection dropping out

My sister just got a new laptop (HP DV6810), and it can connect to our wireless home network, sometimes. However the connection keeps dropping out every 20 mins or so.

The router is in my bedroom upstairs (Linksys WRT54GS) and it is wired to my desktop pc. My sister uses her laptop mainly downstairs but also sometimes in her bedroom which is next to mine.

Anyone have an idea of what the problem could be?

 

Does her computer show a strong signal or weak one? Does the "dropping out every 20 mins or so" happen the same, regardless of which room she's in with her computer?

 

yes, she can be downstairs or upstairs and it will happen.

 

Her computer should show a signal-strength indicator if the mouse is hovered over the network connection icon in the lower right corner of the screen.

As a test, move her computer into the room with router and see whether this still happens.