admin account + website stoped working after sign in

Hi,
I got the user name and password for our website yesterday.
I noticed your service on the our website admin / however, it asked me sign up. which I did.
After that, it did sign in, I browsed your service within the admin page. then I refreshed the page.
It became too slow, and eventually will fail to open. the same thing with our website. it is not opening now!

The website : http://arrow-copter.com

Edit 1: If I removed our website from wpmudev dashboard , will solve the problem ?
I am afraid to do anything now. so will wait for a respond