Wired ethernet network disappears after upgrading to Yosemite

Question

I am a lone iMac on a Windows network, but have connected through ethernet without a problem for years. Since upgrading to Yosemite, however, my network has disappeared. My ethernet is connected, my IP address is the same as before (assigned by DHCP) and I have made no changes to any other settings. The only difference now is that my mapped network drives cannot connect and in Finder, when I click on NETWORK and SERVERS, there is nothing there.
The company IT guy is a Certified Microsoft dude and he swears nothing has been changed in the network. It must be the upgrade.
What has Yosemite changed? (The Firewall is off.)

Answer 1

Found a fix
When trying to fix a wake failure, I simultanuously fixed the issue with network drives. It is connected to the Preferences.
Here is how I could solve the problems:
Press command+shift+c - > Macintosh HD - > Library - > Preferences -> Drag SystemConfiguration on desktop, it's going to make a copy of it (May ask for password, then delete it from the Preferences (which is the initial folder). Shut down, then do a PRAM Reset. If you don't know how to do that :
After you shut down the computer, locate the option, command, P and R from your keyboard. Press the power button to turn it on and quickly press all four buttons before hearing the first 'power up sound'. Keep them pressend until you hear a second 'power up sound'.