Default printer settings are saved under the Devices and Printers Folder, by right-clicking on the printer and selecting Printing Preferences. You will find the orientation under the Printing Shortcuts tab or by making sure the Factory Defaults have not been changed. Click Reset to change them back. If this does not help you, answer a few questions for me please:
1. Are you having this problem on both PCs?
2. Does this happen on every document or does the orientation flip in specifically one program/software or to one document?
3. Did you uninstall the printer before upgrading the PC?
4. Is the printer connected USB, wireless or Ethernet?
