If you reach 100%, you will get a margin call and you will not be able to open any trades. 

Reaching 50% Margin or below will result in a Stop Out. This means that MetaTrader will start to close your open positions.

  • Margin Call: 100%
  • Stop Out level: 50%

In order to maintain high margin levels, you can either extend your equity by adding more margin to your account or reduce the margin you are trading on by lessening the lot size of your positions.