It's probably been said before... but sometimes, it's worth using a plain text editor and not wysiwyg editors.
http://www.textpad.com/ is more stable than notepad and has a much greater capacity. It's got search and replace for multiple files, it can change the case of blocks of text, it has a spell checker..... etc.
If you rely on your wysiwyg editor for doing layouts.... then once you have the layout done, import the html into a plain text editor and at least then you'll know that nothing will get corrupted from that point, except by you.
Textpad is free to download, and there's loads of other plain text editors out there. In the long run, it's worth learning to code from scratch.