Can not add chart on mt4 and open data folder with File>Open Data Folder

I expect the ??? in the path (the user name) contains some non-ascii characters. Some non-ascii characters in the path get replaced by the MT4, though the most are fine. Create a new Windows user with a simple ascii user name and install the terminal in the new user profile.

No need to create a New User. The OP can also setup a separate directory/folder and install it in Portable mode!

1. Ovo: Create a new Windows user with a simple ascii user name and install the terminal in the new user profile.
   Or install it outside of \users\xxx and use portable mode
2. Report it to the service desk.
   • Can someone please advise where I send a Request for Support to Metaquotes. - MQL4 forum
   • Get in touch with developers using Service Desk! - MQL5 forum
   • Report it to the service desk. 'MQL5.community - User Memo' - an article about the algorithmic/automated trading in MetaTrader
   • Report it to the Service Desk, not us users.

I also can not open my data folder. And I read another post of someone new saying the same thing. Looks like a serious bug in this build.

There is no bug. It is a well known problem among many users and it's called P.I.C.N.I.C.

My own experience is that MT4 works fine with a username such as テスト... but only if the system locale (the "language for non Unicode programs") in the Windows regional settings is set accordingly (i.e. to Japanese).

If the locale isn't right, then I get a slightly different problem to those mentioned here. MT4 hangs without even getting as far as displaying its main window. Procmon shows that it is in an infinite loop, repeatedly trying and failing to open the following file:

C:\Users\???\AppData\Roaming\MetaQuotes\Terminal\316B0057FFEE5F4940136557005F8FD9\history\default\symgroups.raw  

But, although the symptoms are slightly different, this is almost certainly the same general issue being reported above. For a Windows username which contains non-Latin characters, the system locale must be set so that those non-Latin characters can be processed correctly. 

This doesn't seem to be a new issue. As far as I am aware, MT4 has always had this requirement about the system locale. 

[All the above from Windows 7, BTW. I can't comment on any differences in Windows 10 as used by the OP.] 

I have been using the W10, and the problem you describe is the same there. The MT4 screws the characters in profile name somehow, and behaves schizophrenic looking for something in the proper profile path and something in the paralel screwed profile path. I reported the issue long time ago.

BTW, MT5 works fine. 

Yeah, full internal use of Unicode in MT5, whereas MT4 is a mix of Ansi and Unicode post build 600.

What does that mean and how do we fix it? I have no strange username either. Just my name.

And a problem like this is a bug or design flaw in the software. Software is supposed work not make you jump through hoops to get it to work.

Software is a tool, and like all tools, they are not perfect (neither are we users). Like everything in life, we are not born "knowing" and we must learn to use tools (or software) properly. In fact, some tools, require formal and official training and even require acquiring licensing in order to be handled (like a driver's license).

Software is no exception! It requires training, knowledge and experience to be able to use it properly, and I am not just talking about MetaTrader, but particularly referring to the OS which in this case is "Windows". Even when the Software is at "fault", there are also many times, when the cause can be the user himself (or herself), and by simply changing a few of our user habits, the "cause" can be eliminated and the problem "resolved".

That is in essence the meaning of "P.I.C.N.I.C. - Problem In Chair, Not In Computer"! Had you used "Google/Bing/etc.", you would have found the explanation yourself, demonstrating the current mindset of most users, of not doing the necessary research and learning in order to properly use their computers and software in general.