The site is down now. Will my balance be lost?
It is ok.
As you can see with the announcements, they are planning to launch the v5.0 later and that's why you can't access the site. There's also a note that you can read that it's part of the launch.
We are on a planned downtime preparing for the v5.0 release./
There is a few hours left until the launch will come, you need wait until it's released.