During the process of reinstalling the 'old' drivers, the modem somehow "resets" to the upgrade (switching on and off, replacing files and registy entries, etc.). You may still need to install the new drivers to take full advantage of the upgrade. Also, see whether there is a new "firmware" for your modem, and ask your seemingly helpful ISP whether it is supporeted.
I am running XP/SP2. To answer this question my profile gives the full description of my computer system.
On Friday when I logged on to my ADSL broadband all was fine, then after about an hour the connection dropped out. I could reconnect, but all day it intermittently dropped out at all different time spans. I rang my ISP - they spent over two hours troubleshooting with me on the phone doing what I was advised to do. They came up with the fact that they had upgraded their line service to there customers and for me to take advantage of those upgrades I would need to upgrade the DRIVERS on my D-Link 200 ADSL MODEM. They sent me the upgraded Drivers via my email, but with their guidance and after uninstalling the existing drivers from 'Add and Remove' the new drivers would not install.
I was then told to ring D-Link and tell them of my problem and ask for help to install the upgraded drivers using the software sent to my by my ISP. The technician at my ISP then guided me to reinstall my original drivers so at least I could get onto the internet until I could get help from D-Link. As it was late in the day, I decided to do this on Saturday morning/yesterday. So I booted up yesterday, was able to connect to the internet, and for 15 hours until I logged off I did not loose connection to the net. Not a thing went wrong. So of course I did not ring D-Link, there was no reason for the call. My question is - Why did this happen? Also this morning/Sunday not a problem. If someone could offer an explanation for this mystery I would be most grateful.