I have a dell 4600c (2.66ghz 256mb ddr, it freezes as soon as i get the dell screen cannot even get to bios but have tried 2 processors and tons of ram and unplugged all that can be unplugged also tried video card instead of onboard also swapped psupply also took out battery and unplugged and hit power to kill cmos and still to no effect anything i have missed please help