First, try to boot your device in download mode, you can do that by:
- Switch off your device completely.
- Press and hold Volume Down, Home and Power, all at the same time.
- Release all buttons when you see the Warning! screen
- Press the Volume Up button to confirm that you want to boot Download Mode
Then, download Kies from here, after you install it, connect your phone to your computer and you should get a message from Kies, ignore it.
On the Kies menu bar, click Tools and then click Firmware Upgrade and Intialisation
Enter the information it requires (Usually, you can find them at the back of your phone) and then Kies will factory reset your phone.
To install Xposed, visit this link.