My laptop starts up but it says the laptop has shut down because of overheating and can only go up to (90d)
then the screen just goes black and nothing works.

Maybe the cooling fan failed? Can you hear the fan spinning before the laptop turns off?

My Dell Latitude E6500 has problems booting. I turn it on and it usually give me the option to start it up on Safe Mode, Advanced Mode, Normal Mode, and ect., but everytime i try to start it up it doesnt get past the Windows Screen so I can’t even log on to atleast scan it. This even repeates as i restart it. What do you think i should do?

Turn on the laptop, press F12 and select Dell diagnostics. Run Dell diagnostics. Make sure there is no problem with the hard drive or memory.
If no problem found, probably there is a problem with your Windows OS.
You can backup data with an external USB enclosure:
http://www.laptoprepair101.com.....enclosure/
After all data is backed up you can try reinstalling OS from scratch.
http://www.laptoprepair101.com.....n-laptops/
Hope it helps.

my dell vostro 3500 displays ‘updating itself and reverting changes’ when power button is switched on.

Let it finish. Maybe the laptop is recovering from unsuccessful update install. Sometimes it might take a while.

my laptop turns on but then it the screen just goes black and it doesnt do anything else , what should i do ?

Take a very close look at the screen.
Is it really black AND blank or you still can see a very faint image?
Did you test the laptop with an external monitor?
At what point the screen goes black? Do you see any image on the screen before that?

My Acer Aspire 5750 wont start, i mean when i press the power button, the power LED just blink 3 times and then off again.

Did you have a chance to test the AC adapter. It’s possible the AC adapter died and the battery doesn’t have enough charge to start the laptop.
If the adapter is good, try removing memory modules. Maybe one of the modules failed and the laptop will start properly when you removed the failed module.

i have Important documents on the drive.

As a last resort you can backup data using an external USB enlosure.
http://www.laptoprepair101.com.....enclosure/
Most likely you have a SATA hard drive in your laptop. It means you’ll need an enclosure for SATA drives.
Alternatively, it’s possible to connect laptop SATA hard drive directly to a PC. It’s using same SATA cables.

Please help me out?