Please let us know how you're trying to access your mail, and with what type of device.
Are you using, say, an Android phone with the default email app (or an app which you've installed). Or are you using a PC/laptop? If so, are you trying to get into your email via Virgin's website or using a dedicated email client, such as Windows Live Mail, Outlook Express or Thunderbird?
Once we know which means of getting into your email you're trying to use, we might be able to work out what the cause of the problem is.