For some reason there are a number of web sites I can't reach on Opera, but I can access them using Chrome or Firefox.
Any reason for this?

I haven't made any modifications that I can remember.

Any help would be appreciated.

Thanks in advance.

Me:

Version information
Version 12.16
Build 1860
Platform x64
System Windows 7

Browser identification

Opera/9.80 (Windows NT 6.1; Win64; x64) Presto/2.12.388 Version/12.16
Paths
Preferences
C:\Users\XXXX\AppData\Roaming\Opera\Opera x64\operaprefs.ini
Saved session
C:\Users\XXXX\AppData\Roaming\Opera\Opera x64\sessions\autopera.win
Bookmarks
C:\Users\XXXX\AppData\Roaming\Opera\Opera x64\bookmarks.adr
Opera directory
C:\Users\XXXX\AppData\Roaming\Opera\Opera x64
Cache
C:\Users\XXXX\AppData\Local\Opera\Opera x64\cache
Help documents
C:\Users\XXXX\AppData\Local\Opera\Opera x64\opcache
Mail directory
C:\Users\XXXX\AppData\Local\Opera\Opera x64\mail
Plug-in path
C:\Program XXXX\Opera x64\program\plugins
User CSS directory
C:\Users\XXXX\AppData\Roaming\Opera\Opera x64\styles\user