Hi, after sending support emails to Asus and to the shop i bought my system from, getting ready to have to RMA it or to pay the shop to troubleshoot, i dug a bit more today and found a way of (apparently) resetting my services to what they should be by default.
I also noticed an issue with the Atheros Bootrom (some Bluetooth thing i don't use), which i managed to reinstall.
It seems, of of these 2 actions could have solved my problem as i've done numerous reboots today without problems.Strange maybe, but i don't care it's now working again!

Thanks for your help Vir!