Sleep mode on Windows 8 - never again!

[Mario1]

Hi guys!
Bad luck Mario here with another weird problem
I was watching a TV show yesterday so I decided to put my PC in sleep mode so I can continue watching from where I paused. Woke up today, laid in bed for like 2 hours or so and decided to finish the 'Royal Pains' attn episode. Pressed the power button, nothing happened - fans weren't spinning, my x-mass tree look-alike was all dark so it kinda made me freak out. I shut down all power to the PSU and tried again - no result.
Had to plug out the power cord, hold the power button & plug it in again just to get the PC working... Got a BIOS CMOS checksum error or something like that
I have no idea if I have to tweak the power settings in the BIOS to get sleep mode working, but I'm not trying until someone who knows his stuff comments here, since I'm obviously incapable of solving the problem myself.

 

[kmo_9000]

Maybe try updating the bios to the latest? All I can think of.

 

[Mario1]

Maybe try updating the bios to the latest? All I can think of.

Running F7 already.

 

[RJARRRPCGP]

Maybe a bad PSU.

I almost forcibly shut my PC down yesterday evening, because when I was running Prime95 large FFT blend mode, I heard the fan stop and saw the power LED blinking. It was just Windows 7's power management that I had to disable.

 

[Mario1]

It's not the PSU, no idea what's causing this.
The BIOS checksum error hasn't appeared ever since, but I have to plug out my power cord if I wanna get the PC working again if I put it in sleep/hibernate mode.
The power button does nothing after the PC enters sleep mode.
BIOS is set up to cache everything in the RAM upon entering sleep mode, pretty sure that's the right option.
Any suggestions, guys?