Just went to the wp-admin page and it defaulted to the login page as it should. A 500 error indicates "The server encountered an unexpected condition which prevented it from fulfilling the request."
If this persists, write down the time(s) it happens, give support a call and ask them what is going on. They should be able to look at internal logs for those times and see what was going on at the time.
Judith "You have to be odd to be number one." Dr. Seuss