If your demo account is up and connected to broker's server, maybe you have to add trading symbols (pairs) by going to: View >> Symbols.
Sometimes the symbols loaded with your platform, are not the correct symbols for trading.
You don't mention your options setup. That is one thing to check.
If you right click on the chart, what window opens? It should give you choices to set different types of orders. When you select an option on this window another window will open with the chance to set size of the order and then buy or sell.
To check your Market Watch pairs, click on the symbols column and get a window that allows you to add, sort, and change info columns for your symbols. For the demo account you may have a limited number of currency pairs and CFDs available. If there are special symbols for broker products then the correct symbols will be downloaded (you have the standard MT4 symbols but some brokers add prefix or suffix).
If the market is not open when you place an order you will get an error message that says that, so this is apparently not your problem.
AutoTrade only impact robot trading orders, not manual orders. It will also impact the updating of an indicator that is controlled by an EA instead of just being a simple indicator.
YouTube has some videos about setup MT5. You can search on YouTube and get dozens if not thousands of videos to help you learn anything you want from MT5 basics to various indicators, systems, and robot trading.
One hint: don't send anybody any money until you have the chance to absorb some of the basics and play around with the demo. People promise riches and show great results on their videos but most of the claims are false. People who make money trading make their money by trading and not getting newbies to send them money. Buying indicators or commissioning new indicators and systems being built is not a bad idea after you get started, but paying money is no substitute for learning yourself and getting some experience.
Check out CODE SHARE for free code to learn with and also check of the FREE indicators and EAs for trading ideas. One of the best ways to learn is to see what does not work, which is mostly what you get with free stuff.
Good luck. PM me if you have some specific question.