So... my SSD was broken. I got it replaced with another 830 and it seems that everything is runnig fine now.
@mediasorcerer
Your suggestion was my last repair attempt ;).
I have similar problems here, but with an Intel CPU and Intel Chipset. My spec.:
CPU: Core i5-3570K
Board: ASRock Z77 Extreme 4
GPU: Gainward GTX570 GS GLH
RAM: 8GB Corsair Venegance
SSD: Samsung 830 Series 256GB
HDD(1): 1 TB Seagate
HDD(2): 320 GB Seagate
DVD: LG
PSU: Corsair HX 750...