What do you do if you log in to roblox and then it just kicks you out?
Solution 1:
That is the kind of thing only Roblox support may fix.
If the game does crash (you are suddenly on your desktop and the game is not on) you might want to uninstall/reinstall the game. Something is corrupted in your install.
I don't know Roblox, but since its an online game we can assume your progression is not saved on your PC. So you will lose nothing.
If the game doesn't crash outright (sends you back to desktop) you might be banned. Then your only option is Roblox support.