I have a Syntax SV266A (that might be the problem), Phoenix Award bios v6.0, Athlon XP 2000, 256 megs of PC 133 SDRAM. The computer post and recognizes HD and CD Rom. I receive a cmos checksum error-defaults loaded. When I attemp to access the setup, I get a black screen, after that the only way for me to get back to the bios screen is by clearing the bios.

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We have had similar problems noted before that turned out to be a bad battery on the motherboard. Since they are cheap, you might want to consider replacing the battery and see if it improves the situation...

Other possible causes of your problem are a virus and a bad MB.