See:

• http://kb.mozillazine.org/Error_loading_websites

You can try to reset (power off/on) the router.

Do a malware check with some malware scanning programs on the Windows computer.
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.

• http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
• http://www.superantispyware.com/ - SuperAntispyware
• http://www.microsoft.com/security/scanner/en-us/default.aspx - Microsoft Safety Scanner
• http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
• http://www.safer-networking.org/en/index.html - Spybot Search & Destroy

You can also do a check for a rootkit infection with TDSSKiller.

• http://support.kaspersky.com/viruses/solutions?qid=208280684

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

I have been tearing my hair out over this...I've cleared cache/history/cookies. I've run 2 different anti-malware scans - both of which found no problems.

I don't know what to do - there are a couple of websites I really need and I know they are ok because they work fine from other computers - I don't want to have to go to my mum's house every time though!

Some ideas of how to sort this out would be very gratefully received....Plain English and idiot-proof instruction please - I am not very pc literate. Thanks!