TwLauncher is TouchWiz, the Samsung launcher. You don't want to uninstall that, even if you could.
To perform a hard reset of the Galaxy SL, turn your phone off. Pull the batter out for a few seconds just to make sure everything is clear. Replace the batter and then press and hold the Volume up, Home and power buttons until the screen flashes. Then release the power button, but keep holding the other two. When you see the recovery menu, use the volume keys to scroll the list of options.
It should look like this:
Choose wipe data/factory reset and see if that fixes it for you.
This will remove your personal data like SMS messages, email, apps and settings but should not touch your /sdcard partition where media files are normally stored, but always make sure you have backups of all your contacts, messages and media just in case.