aliesh said:
Could this have anything to do with the fact that since our son came home he has installed a router so that he can access the internet and also most recently he has done something which means we have shared folders.
No, those will not have anything to do with it, especially if you have access to the internet. That is, unless you get your e-mail from a mail server inside your house. And I highly doubt that as in all likely hood if you did have your own e-mail server you wouldn't be asking for help here

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E-mail works like this:
1.) A person sends an e-mail from their computer.
2.) The mail is sent from their computer to another computer that works as the outgoing mail server. In 95% of the cases, this mail server is located outside of a persons house and is maintained by the ISP (some geeks have their own personal servers).
3.) The mail server then looks at the e-mail address. And sends it to the appropriate incoming server (everything after the @ in the address tells it where to go).
4.) The incoming mail server recieves the mail and puts it in the appropriate account (which is noted by everything before the @ in the address). If the account is not found, it returns the mail to the sender.
5.) When checking your mail, you connect with the incoming mail server. Again in 95% of cases, the mail server is not local and is maintained by your ISP. You login and (in the case of 3rd party software like Outlook) the mail is downloaded onto your computer and stored locally.
A couple things may be the issue:
1.) Your e-mail quota set by your ISP is full. Any messages sent to you will be denied by the ISP. The text of the returned e-mail should give an indication of this. If this is the case, you need to delete e-mail, note that what you see on your computer may not be what is actually on the server. If it is saying your e-mail quota is full and you have nothing in your mail client, you need to directly access your mail. This can normally be done via your webrowser by going to something like webmail.YOURISP.com, what exactly it is depends, contact your ISP to be sure. This may be the case as you are also unable to send mail.
2.) If you are using a client such Outlook for your mail, you may have a in the settings for the account you may have mispelled your e-mail adress. So if someone replies to a message sent by you, it goes to the wrong place. Doubtful that this is the case as you are having trouble sending mail.
If those 2 aren't the case, contact your ISP and see what's up, as the problem most likely is going wrong on their end. And has absolutely nothing to do with you.