When I open a new finder window, there are three diagonal lines that allow you to resize the finder window. Others around me can use this to resize their window but mine seems to be locked. How can I make it resizable?
That should resolve the issue. If not put the plist file back in it's original place (deleting the new one the system generated.
If that still doesn't work, create a test user account. Login to that and test it there. If the issue persists in this test account, you will need to reinstall the operating system most likely.