This is a problem of this mobo you have there
. I've seen a couple of these. Asus tells nothing about such problem but there is.
First what is your CPU and your PCB(and the BIOS version). See the ASUS support list:
CPU Since PCB Since BIOS
Athlon 64 3200+ (Socket754) ALL 1003
Athlon 64 3000+ (Socket754) ALL ALL
Athlon 64 3400+ (Socket754) ALL ALL
Athlon 64 2800+ (Socket754) ALL 1003
Athlon 64 3700+ (Socket754) ALL 1003
Sempron 3100+ (CG version) (Socket754) ALL 1004
Sempron 3100+ (D0 version) (Socket754) ALL 1005
Second: Try to move the RAM chips around the slots (first chip into second slot, etc).
Third: Could be the PSU... what is it? If the 24 pin isn't high enough (20 A from whatI've read somewhere) it may show errors
And fourth: Yeah this board has problems and ASUS still doesn't admit it has. Probably you should write to them asking for a new mobo BIOS chip (they send sometimes). Dunno what else to offer
Good luck
p.s. And Welcome to PCTechTalk