My advice is - If it ain't broke....
My week-old Lion 10.7.2 Unibeast / Multibeast (version prior to 4.1) was working "OK" with only very minor sleep/wake issues. Since I was still finalising my new hack, I thought it worthwhile running Multibeast 4.1 to update some drivers, bootloader, etc.
Unfortunately my computer is now unbootable, and the motherboard doesn't even reach BIOS settings screen. A CMOS reset on the board did reset the bios, but the behaviour remains.
What did I do? I backed up and deleted my /Extra folder then ran Multibeast with only "User DSDT" checked for maximum safety, with the intention of adding additional options on subsequent boots in order to only select the minimum necessary.
Upon reboot, at Lion logon screen, get a KP after 4 secs or so. Restarted and same, KP after few secs on logon page.
Decided to reinstall OS X via Unibeast Lion 10.7.2 USB installer, but computer did not reach the stage where I could instigate boot menu to choose USB - it rebooted during POST. And now only does same:
Power On > Fans spin, mobo LEDs light (for 2 secs only) > Powers down > Automatically restarts after 2 secs, proceeds through CPU identification, RAM identification, responds to DEL for Bios ("Preparing to enter BIOS" or similar) > Powers down > Automatically restarts after 2 secs, etc., etc
As stated, CMOS reset hasn't helped, and have removed all drives, video card, USB devices, etc.
I'm fairly experienced in building computers and this is my third hackintosh. I'm surprised this has occurred because I have not experienced anything remotely like this before.
Gigabyte SKT-1155 Z68MX-UD2H-B3 Motherboard (v1.0, bios v11)
Intel i5-2500K Core i5
Corsair Force Series 3 120GB SSD
Seagate Barracuda 1TB 7200rpm HDD
Corsair 16GB 1600MHz CL9 DDR3
Am replacing the mobo, and will start again. Fingers crossed.