Network Connection Stoped Working

I have a network connection with my PC and Laptop (laptop on XP HE too). Up until this evening everything was OK. All of a sudden it stopped working. It gives an error message something like "The Drive or network connection that the shortcut "my Documents on host.Ink"refers to is unavailable. Make sure that the disk properly inserted or the network source is available, and then try again."
Computers are connected through ADSL. ADSL working OK.
Perhaps you would be able to tell me how to start Trouble Shooting this please?
Thank you.

Hi hmmm,

How are the computers connected via a hub or a router? Try testing the network and see if you can access the other computers this way. On each computer, try accessing the other computer by typing one of the following commands in the Start | Run box in this format:

\\computer (for example, \\hmmm)
\\ip-address (for example, \\192.168.1.101)

Please report back the full text of the error message if you receive any errors.

Thank you for your reply ecross.
I realized that the last digit of my Laptop's IP address had changed and ZA was not allowing networking.
I am very curious though why and how an IP address changes just like that...I would appreciate your thoughts on that.
Thank you.

Your computers on the network is probably set to autmatically obtain an ip address. That's why your ip address changed. ZoneAlarm probably has a way to enter a ip address range, for example 192.168.1.101 - 192.168.1.105. Your other way is to assign the computers on the network a static ip address.

Thank you for your answer ecross.
I have entered the new IP address to ZA and it is now working again.
I do not know how to assign the computer on the network a static ip address.
Thank you for your advice again.