You say you performed a Force Restart. How long did you hold the side power button after quickly tapping volume, then volume down, then press and KEEP HOLDING the side power button. It can take up to 30 seconds, which seems like a LONG LONG time. Try again and don't let go of the side power button for up to 30 seconds. If that doesn't work, you'll need to schedule an appointment at your Apple Store Genius Bar for evaluation and service options/costs - if any. In terms of warranty, the standard warranty is one year, from date of purchase, unless you wisely invested in an AppleCare+ Plan. You must have a sense of when you purchased the phone?
As to data loss, the time to ensure there is no loss of data is before something goes wrong, by backing up to either iCloud or your computer. If you were routinely backup up the phone, your data can be restored. If you weren't and there is something seriously wrong with the phone, you will lose your data.
If the Force Restart doesn't work, here's a link to schedule an appointment at the Genius Bar --> Genius Bar Reservation and Apple Support Options - Apple
