Mac Pro Start up error

Mac Pro - Dual core tower, dual core - quite old, running El Capitan.

I was testing the loop of an HTML 5 animation in Safari, which was just created in Adobe Animate.

The screen suddenly broke up - no response to any command.

After restart I can't start up in safe mode, the screen is broken up with white tiles line covering the screen. The progress bar almost gets half way before freezing.

I have much to do.

Any ideas would be greatly appreciated.