The endless spinning might be an indication of hard drive failure. If the hard drive itself is failing, your Mac will freeze, shows spinning wheel, won't load properly etc. This also happens if the system files are corrupted. We need to identify what the problem is.
Since you already tried Safe Mode, now we can run Disk Utility by booting into OS X Recovery. Restart your Mac and immediately hold down Command and R keys and this will boot your Mac to the Mac OS X Utilities screen. From there, click click Disk Utility.
In Disk Utility, select your hard disk at left column. Under First Aid tab, click Repair Permission. After that, click Verify Disk and if asked to repair, click Repair Disk.
Then restart and immediately hold down Command, Option, P and R keys for 5 seconds and let the Mac boot up. Is it working now ?
Please let me know if that didn't work, so we can continue troubleshooting.