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Thanks for your replies, much appreciated.
Don't know about any conflict Hans, haven't added any new things to my pc and the problem just came on suddenly.
Tried that fender numerous times but it still blocked.
methyl.. I decided to uninstall the F-Secure which is the security for TalkTalk HomeSafe. However, I couldn't find any sign of it on my computer. Did an internet search and came up with a forum on which someone had asked the same question and they'd been given a link to uninstall. I clicked on the link, risky I know, but it worked and now I can get access to the website I wanted.
The customer service woman I spoke to at TalkTalk said that there must have been some problem with the website for it to have been blocked and that I wouldn't be able to access it on any device. Wrong! I used it on my iPad, no problem. She then said 'use your iPad then'. I gave up on her at this point and was determined to find the cause of the problem.
I did what I usually do and search the internet for a solution and found it. Very happy now.