american mega trends bios

my pc config is
mobo: KOB P4M266a NDMx
processor: celeron 1.7
ram: ddr400 256 (MDGBL6F4G2870B1E59 , the mem. is from the blitz company)

this is my sisters pc
she had not used it for a long time.
when she started it a few days ago when the system booted it gave 2 beeps.it is as ami bios .when i checked the net i learnt it is something related to memory.
i cleaned the memory chip but still the same problem.
when she started the pc it booted saying that wrong cmos setting . i checked everything all was fine .i even changed the cmos battery. later when i started it said read error. i even changed the ide cable. then it said ntldr missing .my sister wanted to format the hdd .so i did it and made 2 partitions on one i installed windows xp it is working fine. when i wanted to install windows xp home on the other partion the loading stopped saying that my system does not have enough memory or my cd is corrupted .i tried using the xp cd on another pc and it loaded fine. then i even changed the ram on my pc but it still it gave the same error. saying that the memory is low. why is it happening even though i have enought memory 256.why is the system not recognizing the memory when i try to install windows xp .i tried all the other os but still the same problem
when the system boots as i told u earlier i get one beep but when i get the mercury logo i get the other beep. the other thing is that when i boot the system some screen pops on the monitor something related to frequency. i t goes off fast so i cant read it.
can anyone help on this .
thanks in adv.
where can i download a manual for the mobo. any site ?
do i have to upgrade the bios if yes how can i do that.