"Unfortunately Application Installer has stopped working" I was facing this problem few hours back. I had this problem after failing setting up lollipop custom ROM on my device. It was seeming to be a freaking problem as I could not find out any specific solution searching the net over hours. But finally I found out a solution. It worked perfectly on my Samsung Galaxy Core 2.I hope it will work on your device too.
First of all you have to go through factory reset. I guess u did that.
then You will need to install stock ROM of your device, for that u wanna download your device's stock ROM first. U can easily find your stock ROM here-> www.sammobile.com
For installing the ROM u ll need a PC software named Odin. You can find it here->( www.mediafire.com/download/czliot4z9zptt5z/Odin3_v3.09.zip)
You will also need the USB driver for your device. Download from here-> (mediafire.com/download/403l9lozr5ij9ad/SAMSUNG_USB_Driver_for_Mobile_Phones.zip)
Now you wanna extract all the downloaded zip files.
After extracting the zip file of stock ROM u ll get a file which is a tar file with a extension of md5(tar.md5)
and after getting the zip file of Odin software extracted you will get a file.
Install Odin from that file.
Install the USB driver too.
Now boot your device to download mode by pressing Volume down Key+Power Key+Home Key button simultaneously. In download mode press volume up button to continue.
Now connect your device with a USB cable
Now run Odin as device administrator. After opening Odin, you will get there many kinds of selective tabs such as BL, AP/PDA etc.
Now click on AP/PDA and select the previously extracted (tar.md5) file. MAKE SURE RE PARTITION IS NOT CHECKED.
If you have connected your device properly you might get a message in the log field like <*>Added.
Then click start to start installing the stock ROM.
Next step -> Sit back and have a cup of coffee or anything else. After a while you will see a green colored message "pass" in Odin. You will also notice your device getting restarted by itself.
You are done... Now your device is just like the one you bought earlier.
Let me know If the process was useful.