If when you are on MetaTrader, whether it be on desktop/laptop or Mobile/Tablet device and you are logged in and can't open a trade, make sure that you have logged in using your Trader Password and not your Investor Password.
Trader Password: Gives you full control over your MetaTrader account. Meaning you can open/close trades, set Stop Losses etc.
Investor Password: You will not be able to open/closes any trades, set stop losses etc. This password is usully given to individuals you would like to have a look at your trades but not be able to action anything on your account.