
On Monday, Skype users began experiencing outages of Skype services including signing in, making calls, and sending messages. One of the sure ways of telling you have a problem is after signing in, yourself, as well as all of your contacts, appear offline when you know that's not the case.
The problem has been ongoing almost all of Monday morning, but fortunately is only affecting regular users and not enterprise users, meaning large businesses relying on the software can continue about business as usual.
Microsoft says that they are working on the problem and will fix it with an update "soon," although no solid ETA has been released. The issue has been identified as a "network" problem:
Source: Microsoft