Not sure if anyone else has had this but, after about an ingame day and one skill point alocated, when I open up the skill menu it makes my charatar look all the way down and I can't see the menu.
The reason isn't related to anything on the actual page itself, You likely used the Carriage, or perhaps hit some sort of physics variable wrong.
Your character model is actually, technically not positioned right, even if everything about what you see looks right, and this affects how your character "puts up their arm and holds a piece of paper in front of its face" - head on over to http://mlbs.slipcor.net/ and download one of the last two versions of their Save game fixer applet.
I think the last version actually has all the features on it, but the 3rd version is the one that specifically helps your issue.
"reset player model" doing this should fix your sheet issue, as well as any other misc issues that you might not be aware of happening related to it.
"Reset horse and waggon" can assist in fixing issues with the horse that may (likely) have caused the character issue in the first place, however, ultimately, you're recommended to not actually drive the cart until a later time, as its known to be quite buggy, still.
What do you use to run the .jar file?
If you can't just double click it/execute it/run it
It is used by Java, which most people have installed for other reasons than MLBS - JAR is a Java archive and while not all of them launch their own applet, some, and these ones, do.
I think in the event that it doesn't automatically open on its own, it means Java isn't pathe/ pathed correctly - which doesn't stop Java itself from running, but does prevent a decent amount of discovery.
You can try and just tell Java to run it, or you might try looking up how to path Java so that you can just run it without telling Java to do it.
Or you can try and wait for Slipcor to take advice on the matter for the fixer.. I feel like I remember seeing a comment somewhere talking about using it in alternative ways...