My Macbook air laptop sound, fan and speed is messed up, how do I fix it?

Question

Where do I start. One random day I came home to find out that my sound has been muted. I tried to fix it with headphones, reseting the PRAM, google, and even by asking my schools computer tech. Some times the mute button would disappear and the sound bar would be in color but their would still be no sound. After  the computer tech went on his account on the laptop to un-mute it, which he couldnt, he told me that my built in speakers dont work and would need to be replaced next year. Im like okay no problem, that same day i closed my laptop and found that the light was still on, I asked a friend and he said the black bar between the keypad and screen is what activates the laptop to shut off, which means its broken, so in between class periods i either shut down my laptop or put it to sleep. The next day my laptop starts to run slow and as soon as i power it on the fan runs immediately but the laptop isnt hot. My mouse moves at normal speed but my applications are running slow. This all happened in one week which is this week. My battery dies at a normal pace though.
More information
This is a school given macbook air for a magnet program called iPrep, so i cant download anything with our administration password
This is my second laptop out of the 3 years ive been in the program. My first laptop started to break after the sound got muted and my laptop ended up with an X on the battery and would only turn on when a charger is plug but would go super slow. This makes me scared cause i dont want that happening at all to this one.
Problems
Sound is muted, it sometimes un-mutes but there is still no sound, internal speakers broken
When closed the screen display is still open
Computer applications go slow, fan turns on immediately
Any help, this is bothering me so much

Answer 1

Hi Jollified,
Does your sound work when you try to use head/earphones? If so, try the following:
Plug your Headphones into your Mac.
Play a sound through them (a song for example), then stop the sound.
Make sure 'Preferences' is isn't open. If it is, Quit.
Launch System Preferences > Sounds.
While the Sounds tab is open and set to 'Headphones', pull out the Headphones from the jack.
You should see your Mac reset to 'Internal Speakers'
Also, I see you have tried resetting the PRAM, have you tried resetting the System Management Controller (SMC)? Resetting the System Management Controller (SMC) on your Mac - Apple Support
As for your MacBook not sleeping when you close the lid, there are many reasons this can occur.
First of all, check out Apples article on the issue: OS X Yosemite: If your Mac won’t go to or stay in sleep If you find these steps don't help, try a few of the following:
A common cause for the Mac not sleeping is your printer. If there are queued jobs waiting to be printed, but your printer is switched off, for some reason you Mac just wont like it and simply will not go to sleep. System Preferences > Print and Scan > Open Print Queue
Do you have an Ethernet Cable connected? People have reported in the past that removing their Ethernet allowed their Mac to sleep. This goes for other things you may have connected directly to your Mac also.
Try heading into your Mac Preferences > Sharing and deselecting 'Internet Sharing' as well as 'Printer Sharing'.
Also deselect Wake For Network Access by heading to System Preferences > Energy Saver > Power Adapter > Wake For Network Access.
Energy Saver > Schedule > Startup or Wake - Uncheck.
Alternatively, set your system preferences to Never Sleep, and put into Sleep manually: System Preferences > Energy Saver > Computer Sleep > Never.
Good luck!