It has to go to a repair shop, it's (evidently from your question) not something you can diagnose, so we can't guess what the fix is. A blue light getting brighter and dimmer means "storage access" (like the "hard drive light" flashing in a PC), but a solid blue light could be caused by any number of failures.
If you can boot into download mode (Volume-/Home/Power), you can reflash the ROM (which will delete everything, but it's probably already gone, so I hope you have backups of anything important). See
[Samsung] How to flash Stock ROM via ODIN.