[SOLVED] - Macbook Air Sleep/Wake problem was caused by a stuck Mavericks update
Macbook Air behaving like it is in some sort of a permanent quasi-sleep mode and you run OSX:Mavericks? It may be that you had an OS update and didn't get to "finish" so your laptop is stuck in mid-installation of its update - only you can't tell that because you can't see the screen.
Here's what Apple Support had me do the first time I had this issue. I've just done this again after another update caused the same symptoms today:
1. Boot into Safe-Mode by shutting off the laptop - hold the power button until the screen goes completely black.
2. Turn it back on while holding the Shift key and Power button together - the screen will come on as if it is doing a normal boot, but keep holding the keys together until you get a progress bar at the bottom of your screen. When you see the progress bar, release both the keys you were holding. This will take a few minutes and your screen will eventually go dark again as the progress bar processes. This is expected.
3. When the screen darkens after step 2, you will be at a login screen you cannot read due to the darkened screen.
4. Wake it up - but don't type any letters or spaces which might interfere with getting the login correct. I wake mine with a very quick press/release of the power button. When I see my mouse pointer I know the laptop is awake.
5. You are now going to log in, but you'll be typing blind so take your time to know you got it right - if you mistype you'll have to redo all the steps so far before continuing if you are unable to correct it first.
6. Type the FIRST LETTER only (not the full name) of your normal login account and press the Enter key.
7. Type your password for your normal login account and press the Enter key.
8. Wait until you see either the mouse pointer turn into a color wheel and/or until your screen either goes dark again. The system is processing your login so you won't know if you did it right until you see the color wheel (go to step 10) and/or the screen darkens (go to step 9).
9) If the screen darkened, wake it by pressing the spacebar
10) You should now see the Mavericks installation screen - proceed through its screens until it finishes its installation and you are at the desktop. If all seems normal, you are done (although I did a clean reboot at this point just to make sure all was good). If not, proceed to step 11.
11) If you are looking at a desktop configuration that isn't what you are used to seeing, open a Finder window and then use the keyboard shortcut for the "Go To Folder" (Cmnd+Shift+G)
12) Clear whatever is in the field that opens up and then type "/Users" without the quotation marks. Press the Enter key. This should change your finder to your laptop's User's folder.
13) If you see a folder with your normal login name that you cannot snoop through without being told you don't have permissions, you are probably logged in as a guest and should log out or restart in order to log in normally. Once you do so, you should be at your typical desktop configuration.
Good luck!