By "access it", do you mean "open it" by double-clicking an icon? If so, that's the normal way to open an HTML file. RIght click on the document's icon and choose "Open With>" to use Notepad to open it.
If Notepad isn't on the list, it's a bit messy to get it on there, but you only have to do this once:
1. Right-click on the icon, and hover on "Open with >" to get a menu, then click "Choose default program..."
2. IMPORTANT: Uncheck the "Always use selected program to open this kind of file." box.
3. If Notepad is on this list, double click it and you're done. If not, the click the "Browse..." button.
4. In the directory "address box" on type, type "%SystemRoot%\System32" and press Enter.
5. In the filename box, type "notepad.exe" and press Enter (or scroll down to "notepad" and double-click.)
6. Now Notepad should have an icon in the "Open with" dialog box. Double-click it and you're done.
After that, you'll just right-click, open-with and choose Notepad.
By the way, that "All Files" isn't an actual file type. It's just used in open and save dialogs to let you see all files of all types that are in the folder (directory) you are working with.
There's a small tweak that anyone doing programming on Windows ought to consider. By default, Windows hides the file type extension on the file names. I prefer seeing exactly what the file name is. To do that, click Start and in the search box type "Folder Options". You can also find this in Control Panel, but typing the name is usually easier. In the "Folder Options" dialog, click on the "View" tab, then uncheck the "Hide extensions for known file types" box, then click OK.
From now on, you'll see "project1.html" or "project1.css", etc. so you know exactly what you're looking at. One bit of caution, though. This makes it easier to change that filetype extension in a rename, which makes it harder (or impossible) to open the file properly until you rename it back. Windows 7 added some assistance by not highlighting the type in a rename operation, but you can use arrow keys to defeat that. Don't do that, except if you're fixing up a previous bad rename.