Thanks linuxmint7, unfortunately that's the exact way it's set up now so that's not the problem.
I'm getting error messages for any page I try and open with Opera - can't even open yahoo. Anything I type in to search when page opens I get a security issue box saying 'the server's certificate chain is incomplete and the signers are not registered'. The pop up alerts appear many many times and appear to be going through different parts of the yahoo page - ads.yahoo.com, au.search.yahoo.com, us-mg.mail.yahoo.com etc etc. Even if I click on 'approve' in the box there are so many of them it's ridiculous and Opera is unusable. I didn't even realise it was other pages as I only tried to login to facebook (I rarely use Opera) but something is very wrong with Opera on my desktop!
I have full internet security, run malwarbytes and superantispyware also and my system is apparently clean, Windows 7 64 bit, and don't have issues with any other browser but Opera. Any suggestions?
Thanks!