I purchaed my S6 tablet today. It has been on it's fast charger for around 4hrs and only shows the Samsung logo. After 3hrs, I removed the S Pen from it and the Keyboard case. Again, only the logo. The last 30 mins, I removed the charger to maybe allow it to restart of it's own accord.
Sorry to hear about your issue! That must be a bummer cuz you've only just got the tablet. My first bit of advice is to shut the tablet off (by holding Power+Volume Down to perform a Simulated Battery Disconnect), and then hold Power+Volume Up when you see the Tab S6 logo. Once you've done this, you should be in Recovery Mode. Use the volume keys to select Wipe Cache Partition, and use power button to enter it. Confirm the action by selecting Yes, and then try rebooting your tablet. 9/10 this has solved issues I've encountered like this.