Start while holding the Shift Key.
Starting in Safe Mode, just loads the absolutely necessary from the OS to run, no user things.
It is enough to start in safe mode and shutdown, it "resets" everything, and often solves issues just by doing it and then restart.
Your problem is probably that all disk space is used up. 11GB is low when you also need buffers caches for apps that run. If this "heavy app" is also in the startup list, then it will be very difficult to eliminate it.
What is this "heavy app"?
Post the result, and give all details of your MBA, model, year, disksize and HDD or SSD, OS version....
Thanks for your help. It seems like safe mode does not work on my Macbook. Nothing happens when I hold down the shift key and turn it on. It just turns on naturally and turns of after the apple logo apears.
However my MBA is 13", 120gb HDD. and OS version is 10.8 i think, actually the latest one. I bought it 7 months ago.
Do you have any suggestio to fix it ?
The MBA bought new? Then you have warrantee.
You should be able to start while holding the Alt(option) key for the Boot menu: HDD, RecoveryDisk.
And start while holding the Shift key for the Safe mode.
Do the SMC reset:
Do it twice or even three times.
When you can then boot into the safe mode, do that, then shutdown and do the PRAM reset:
When the system then still misbehaves, go the Apple, make an appointment and have them look at it.
Thanks for your post. Actually for some reasons safe mode never appears for me. I tried the rest but did not work. I have already booked an appointment to check it at Apple. However, in Disk Utility, when choosing the location of the new image, I can browse in my disk and could see all my files. So I think thats a clue that the HDD is fine and my files are still alive. But do not know if there is any way to copy them.