You might not be looking at your inbox.
Particularly with Windows Live Hotmail's new interface, it's easy to overlook which mail folder you might have selected. If you've accidentally clicked on a folder that has nothing it, like "Drafts", it might appear that your inbox is empty. Before panicking, click on the "Inbox" icon on the left to make sure you're looking where you think you are. This also clears "full message view" which can obscure the list of messages in your inbox.
You've selected a display filter.
Next to the "Sort by" item in the Windows Live Hotmail column header is a small icon that allows you to "Show only messages..." that meet a criteria. For example you could elect to show only messages that have an attachment. If there are none, then your inbox will appear empty. Once again, clicking on the inbox icon to the left will clear the filter and show you all messages in your inbox.
It just disappeared for reasons unknown.
I hate to even have to include this as a possibility, but as best I can tell it happens. Recently it seemed to occur as accounts were switched from the old style MSN Hotmail to the new Windows Live Hotmail, but that should be over by now. Nonetheless, I've not been able to determine a common cause or reason. It just happens
You can try to contact customer support. The quickest route I found was this link: https://support.live.com/eform.aspx
, and then click on Windows Live Hotmail. You can then submit a support request.
If I could be of further assistance, let me know. If this helps or solves the issue, please rate it.