You can reinstall Lollipop by installing ODIN onto your computer.
and then you download lollipop, that is compatible with odin, for your S5 HERE.
Your model number for your S5 on the phone underneath the battery. You search that on the website.
These are the steps you do next
- Turn off phone.
- Hold the Volume Down Button, Home button, and Power button.
- Ignore the warning message and press the volume up button to continue.
- Connect Phone to Computer
- Allow computer to install drivers.
- Extract the ZIP file of Lollipop into the ODIN FOLDER.
- Open ODIN
- Click on the PDA button.
- Select the extracted *tar.md5 file.
- Click Start!
- You should be running Lollipop before you know it!