On Windows?
Where did you install Opera to? Did you accept the default installation path of "C:\Users\yourusername\AppData\Local\Programs\Opera" or did you change it?
You can delete "C:\Users\yourusername\AppData\Roaming\Opera Software\Opera Stable" and "C:\Users\yourusername\AppData\Local\Opera Software\Opera Stable" (while Opera is closed) to start setup over again to see if it works this time. If not, there could be something external from Opera interfering with Opera's reading and writing to those folders. Could be your anti-virus for example that's interfering.