looks like you're just running the basics... but that 300w power supply still seems pretty low. especially considering it's not an antec or enermax or other HQ manufacturer. I'm not positive this will fix the problem, but it's something that needs attention anyway. imho, you're just asking for trouble if you "eh, it's good enough" this.
recommended reading...
http://www.firingsquad.com/guides/po...ly/default.asp