Strangely the same thing happened to me today, during the CQ VHF contest, of course! My waterfall is blank and I see no signals. But I was transmitting deaf and got reports 100 miles away.  My netbook (Win 8.1) reports a problem with my Sabrent dongle which has worked for over a year until now... So I just ordered another one ($8). Nothing else has changed. So I hope that is it.