Just to make sure your installation is similar:
This is how I installed PG:
- Created a folder call powergallery
- Gave it full permissions
- Created Database through cPanel
- Added user with full permissions to the database
- Uploaded PowerGallery into the newly created powergallery folder
- In browser, went to domainname.com/powergallery/install
- Followed setup wizard
Did the installation wizard give you all green checks?