Hi blizeH,
The issue could be due to an application or a driver as the system runs properly in Safe Mode and with services disabled in Normal Mode. Vostro 430 supports DDR3-1333MHz PC3-10600 modules and the Crucial modules seems to be compatible as per the information provided on their website. You can fix the RAM modules to any three continuous slots. I suggest you to run a thorough virus scan to check for any possible infections and let me know about your findings.