ifixit.com has lots of guides. you question doesn't give enough detail to pin point which version of the macbook air you have, but you can find lots of info. It's not a simple machine to work on.
StartUp sound is good for your system because it will tell you something but if you want to turn it off then try to
press the F10 key on your keyboard to mute you Mac before rebooting or use any app for it. if you want to know the importance of startup sound than follow Apple Support Number .
: well hold down the home button and bunch of x's will show up press on the x on the app u want to delete and it will say do u wanna delete this app press delete and BOOM its deleted
well if u don't have safari on it already then I don't know what to tell u but a good option is to find the apple company closest to you and find their number and call them and ask them or schedule an appointment and go up there to the apple company and take you apple MacBook air with you and show them what you are having a problem is with it on safari that's all I can think of now but if I think of something I will tell you..
This is a known issue with users sending PDF's using Microsoft Outlook. The link below gives instructions on how to change on their end.
Link:PDF file changed to DAT file on receiving end when using Outlook in...I also found a solution that might work on your end...This is from a blog post on the Apple forums.
This is a common problem.
I have found a converion web-site www.winmaildat.com, where you upload the problem file, and it is automatically 'deciphered', and the contents can be downloaded in their individual files.
The Best Program I have found that I use ALL THE TIME to free up Hard Disk Space and increase the speed of my Mac is CleanMyMac2. Link and Video Review Below.
Link to Website:CleanMyMac 2
It is not a hardware problem and easily solved by technicians. If you don't have enough knowledge than try with any Mac Book Expert. Mac Book technician will guide you step by step for reliable solution. Follow https://discussions.apple.com/message/24231664#24231664#24231664 and Mac Help .
It was the most common MacBook Pro intermittent black screen problem may be due to motherboard out. Get contact with your nearest Apple Store and Fix it. Follow http://support.apple.com/kb/he5 to see your country Official Support Contact list and for more help
Apple Customer Support .
Communication between your computer and disk drive have failed. Try a different disk. If you lower the burn speed it may help you get the job done. Put it to about 24X and see if that works.
In Pages under the "File" menu there's an "Export To" selection that has Word listed as an option along with other choices. I'm using the version 5.2 of Pages, so your's might be different.
You have set a password for it. If you cannot recreate it. You can call Apple. They charge $20 on most calls. Might give you a freeby on this problem. You will need the serial number on back of machine which I had to use a magnifying glass to read. Good luck
Sound like you have an issue with either your hard drive or the operating system has lost the plot. Try this OS About OS Recovery
If you are able to access the recovery partition then use the disk utility to check the disk.
If this does not work then take the computer to an Apple repair centre, if it's still covered by warranty the disk might be replaced under warranty.
If it's not covered, you could try using DiskWarrior 4 The Disk Utility for Mac Disk Repair Mac Directory Repair... which has allowed me to recover disks that have not been able to be repaired with Apple's disk utility.
