hmm how do you connect to the net again ? dial up ,cable ,dsl ,other ?
How are you setup
1) internet connection - broadband modem - router - pc (router dials out)
2) internet connection - broadband modem - router - pc (dials out)
3) internet connection -broadband modem - pc (dials out)
And if your running a software firewall on the pc please note that on the option and two is this a wired network or wireless ?
possiable reasons and solutions:
Reason and Solution #1:
I have noticed that some cheap routers lock up when they are over worked if your playing civ and downloading something this may very well be your issue you can test it by directly connecting the broadband modem to your pc and using the isps dialing software to make a connection.
If the above fails check your tcp / ip stacks they may need to be uninstalled and reinstalled they become corrupt on some rare ocassions.
Reason & solution #2:
If your on wireless try moving the pc or the router closer to the other and make sure there are not to many walls or floors between them especialy ones with alot of pipe or duct work they can and will dampen the signals a bit.
Reason & solution #3:
Driver conflicts or corruption download the latest drivers for your nic card and install them.
Reason & solution #4:
Scan your pc for viruses and spyware if you need a list of freeware apps see this post on my forums
Here.
also run system file checker click on start then run and type
sfc /scannow (you will likely need your xp disk)
At this point we have pretty much targeted nearly everything that could be wrong with your pc and network that would cause you to lose you connection.
After this your other options would be to check the phone or cable lines in your house if your on DSL make sure all the phones in the house have signal splitters on them otherwise all it takes is somone to pick up a phone with out one and you will lose connection.
Make sure you run a good quality extension from the phone jack to the modem like [KC]Bantams suggested you can buy a broadband certified one at a local pc shop.
And if you know a bit about phone wiring you can pull a cable from the phone box in your basement to your pc like I did so you know it's done well.
at this point we have covered your pc ,network and house pretty well and I would suggest calling your isp.
****If your running a software firewall please note that some will lock down your pc if they feel it's being attacked giving the appearence that your connection is down when infact it's just being blocked so disable your soft firewall when this happens!!!