Been there.
Can the laptop "see" the network at all?
Start - My Network Places - Entire Network - Microsoft Windows Network.
Can you see your network named there?
If so, double-click it.
Does the "other" computer(s) appear?
If so, click it.
If you get that far, and then get a message about access being refused, it's a sharing permission that's got changed, or it's something in the Administrative Tools section in the Control Panel.
If you get there and it lets you browse the other computer, try opening a folder there, and if that works go back and see if the problem has gone away.
Let us know what the results of the above are, and someone is bound to know a next step.