Every time I make a move in lessons, my computer shuts down.

I can't think of anything on the website that could cause your computer to shut down. 

Maybe your computer is embarrassed for your moves... Just kidding, I can't think of any reason either why this would be happening.

is your computer naked? give it clothes. or at least a underwear and/or bra

why r u clownish on me, penguin?

Thanks for the serious answer, Martin. Guess I'll have to ask a computer tech. Jeesh, I didn't expect so many other, immature answers. I guess a lot of children use this site.

It could be caused by a bazillion different issues. This is probably the reason no one gives you a very straight answer; it is virtually impossible to guess what is wrong from the limited information you provide. 

Perhaps it's an issue with your network settings, your OS and/or your current java client (if chess.com even runs on java that is; I don't really know and I'm too lazy to go find out).

It could also be your system overheating and it could be your network configuration that is having a bubble. Anything in between? Yes. That could also be it. 

If I were you I'd consider reinstalling my java client first off in order to see whether or not it is the culprit.

Then I'd proceed to reinstall the OS. That's basically what I always do when I don't know what the problem might be, and this method usually works although it is a crude way of resolving issues. Remember to back up your data first

If that doesn't work (which I strongly suspect it will), maybe it is time to have a look at the hardware. A modest guess is that it has to do with either your network card, your motherboard or your RAM. 

You could also have a rouge or malware browser extention. Try using a different browser.

When Chess.com went to Version 3, they stopped using Java, so I doubt that's the cause of the problem.