I returned after an hour and the system was in sleep mode as it should be (it didn't get into sleep mode before). Tried to wake it up and the system started to reboot every 1 second (no posting at all-blank screen)
Sorry based on the description (which I'm sure is clear to you) didn't realize the system is now permanently in a restart loop.
Board is only a little more than 5 yrs old.
No onboard video so you cannot test with GPU removed.. ok
Remove one stick of RAM, leaving just 4GB (single DIMM installed)
Remove the GPU
Disconnect 24 PIN connector
Perform a CLR_CMOS again, install jumper and wait a minute
If you want to be thorough, you can take the MB battery out and test it as well.
Remove CMOS jumper
Reinstall battery
Install GPU
Connect power and attempt POST
If you continue to get the same behavior, you can remove the board from the case and bench test. How much time you want to spend after this is up to you.