I have a sentence with the word "ASP.NET", but half of the word doesn't fit in the current line anymore. There is no hyphenation which is quite ok, but latex doesn't insert a linebreak before the word, instead it is overlapping the margin. I suppose this is happening because of the dot. How can I control the linebreak dynamically to avoid overlapping?
Load the package
microtype and that's already all you need. If not, you will have to decide which breaking-point you want to allow and add it (e.g. ASP"-.NET). I would not break after the dot: A dot at the end of a line always looks like the end of a sentence and ".NET" is kind of a fix expression which should stick together.
When your document is finished (see darthbith) command, you could try to rephrase ("...using ASP of the .NET framework...") or push the word to the next line with a new not indented paragraph or alike.
If you want to have a line-break without a hyphen, you may want to look here or use some short-hand of the package
babel. This depends on the language you are writing in.