Three suggestions to help you sort out your Yahoo Mail issues:
1. Carefully check your email address for typos. It is easy to make a mistake, which would result in you not receiving the test messages that you've been sending to yourself.
2. Check your spam folder to make sure that Yahoo Mail didn't put your messages in there. Yahoo Mail will often flag non-spam messages as spam for unknown reasons and then put them in the spam folder.
3. Check your Yahoo Mail settings to make sure that you do not have your spam folder set to immediately delete all spam messages. If this is the case, then if your test message is flagged by Yahoo as spam, then redirected to the spam folder instead of the inbox, those messages would automatically be deleted without you ever seeing them. That could be the cause of your disappearing messages.
Also, it is important that you sign in to Yahoo Mail at least once every four months, in order to keep your mail account active. If you do not do that, Yahoo Mail will designate your account as being inactive and flush all of the messages in your account after that.
Sorry to hear about your Yahoo issues. Mine was the absolute reverse, getting as many a 35 "spam" emails per day. Mostly a bunch of swindlers looking for personal info, so they can take you to the cleaners.
Yahoo was my very first (personal) email account, over 6 years old, tonight I cut the ties for good (due to the serious spam issue). I have 4 other email accounts, so I'm good.
As etalmar pointed out, are you regularly checking your email? Did you write down the details (logon name & password) during signup? If you aren't getting emails, perhaps you (by mistake) are giving out the wrong email address. One way to check, sign up for a product that requires email verification prior to using it. Also, when you joined this forum, you should have received an email from Windows 7 Forums, welcoming you.
Hopefully, you'll get Yahoo up and running for you.
My account is for sure "ACTIVE" since i use it for myfacebook contacts, means i use it every day for the last 2 years.Also my spam folder remains "18 spam " without any change! No new spams- no new meesages , no facebook messages. Of course , i had report as spam an account of a riend in facebook because every time someone adding a comment in HIS wall , i was recieving INFO in MY yahoo BOX!!! About 20 messages !!!! not MINE ...
Perhaps as a result of your reporting your friend spamming your Facebook and Yahoo Mail accounts, Yahoo may have temporarily put a freeze on all incoming mail, until they can sort out your complaint. Just speculation here, but it may have something to do with the sudden absence of any mail messages in both your inbox and spam folder.
You could try contacting Yahoo Mail support http://help.yahoo.com/fast/help/us/mail/cgi_feedback and explain to them that you are not receiving any mail. They may be able to determine if there is a problem on their end and offer some suggestions, although I should mention that their support can be on the slow side more often than not.