Pending Order stuck

I placed an order for some shares around 15:35 today. I had enough free funds in the account but the order still had not been executed by close of the market at 16:30 and the price had not changed since placing the order. Is anyone aware of any issues today with trading at all? Is there a limit a non professional account can buy? I did not set up a limit order, so it should have executed it even if the price had gone up as i had enough free funds.