Can’t log in with password-PLEASE HELP

I don’t know what happen but all in a sudden, I can’t login to my admin panel – it was still working fine 3 days ago! I click ‘lost password’ but it says “Sorry, that key does not appear to be valid.”

Can someone help me – I need to get into my blog urgently and I don’t know how to fix it. I’m currently on version 2.6.