Personally, my Last.fm does not open for about 6 hours. However, official information appeared just an hour or half an hour ago. The following note was posted on the service page on Facebook:
Hey folks. The site is currently running down to one of our data centers. We have staff on site, bring things back up.
Hi people. The site is currently down due to a serious power outage in one of our data centers. Our employees are on site, engaged in restoration.