1. The default Ubuntu drivers should work fine.
But Intel also has up-to-date Linux drivers on their web site:
<= RTL8169 driver should be fine for your RTL8111d on-board NIC/Intel DG41TY mobo
2. Since you've apparently got a multi-boot system, and since the NIC apparently works in Windows, it's probably NOT a h/w problem (good!)
3. Please try the following:
a) DELETE your network interface
b) Reboot Ubuntu
c) Try auto-detect/auto-configure
4. If that doesn't work, please:
a) Run "lspci", see if it detects the device
b) Run "dmesg", see if there were any errors/warnings at startup
c) Look at /var/log/messages syslog, see if there are any errors/warnings
d) Run "insmod", see if the correct RTL driver is loaded
Please post back what you find!
Your .. PSM
My experience is that the new GUI "NetworkManager" doesn't always play nice with old-school "ifconfig" style manual configuration. Focus on one or the other (cmd-line or GUI), but don't try to mix'n'match.
Frankly, I'd encourage you to use the GUI exclusively - at least until your network configuration is stabile again.
If you've ALREADY got your network working, then please mark your thread "SOLVED".
As to *why* the problem occurred - all I can say is "Sometimes, ca-ca happens