It is odd that the system was running fine then suddenly would not boot, most often when I have encountered a problem like this the issue has been with power. Memory, CPU and motherboards failing usually exhibit more symptoms before the failure. It isn't unheard of for a system to suddenly fail with the PSU still being good but I would also look into the power supply, the system may have a bad 3.3v rail or one of the power connections is making poor contact. Try reseating all the motherboard power and then clear CMOS again. If all this still fails then you can try another PSU to see if you get the same issue.

The problem could be, in order of likelihood (in my opinion):

1. Power supply

2. Poor CPU contact in the socket

3. Motherboard failure

4. All your RAM has died (not likely unless you PSU also died and sent a spike into the RAM)

Luckily you should still be under warranty so if anything has actually failed you should still be able to get it replaced.

Good luck.