Has me beat. Perhaps some of our more experienced members have an answer for you?

Could you explain/describe this 'crash' you're having? Is the machine actually locking up? Do you get an error message? Or do you just become unable to use the internet? Will the machine run fine in all other ways?

How are you connecting to the net? Dial up? Cable? DSL? Do you have a router and an ethernet card? Or DSL/Cable USB modem? Any information you can give in this area will tell us a lot, and could help someone figure out what's going on.

Something could have messed with your drivers, or messed with your network settings. Or any number of things. A bit more info could uncover something.

Is your modem connected to a network card in your computer? Or a USB port?

If it's connected to a network card, I'd consider removing the drivers for the network card by removing it in Device Manager. When you reboot, you will have to reinstall the drivers, and then, Windows will automatically reinstall networking protocols. If you are lucky, one of these files are what has been messed with, and restoring Networking to it's default state will fix it. Hopefully. Cross your fingers.

So you know, this is a longshot at best, but you seem to be in a desperate position, it's beginning to look like 'reinstall time', and I take it you'd rather find some other way to fix this.

If it's a USB modem, I have no real experience with them, I can't think of anything suitable short of deleting all TCP/IP networking protocols, and reinstalling them from scratch.

Got yourself a real stumper of a problem here, gotta say it, Chef. :(