Thank you for your post.
If after the hard reset you are still experiencing problems, please plug in your Nokia C5-03 to your computer via usb and install(or reinstall) the latest software version using Nokia Suite.
I have problem with my Nokia C5-03, when you want to unlock the phone, pressing the Unlock my phone will not be unlocked, so I try ten times, then we can unlock, do a few minutes and after that normally blocks the entire phone, which can be a problem. Sorry for my bad English.
You may try the following steps:
Hope this helps.