memory benchmarks w/ sandra problem!!!!!!!!!!!

win2000 XP
256 DDRam PC2100
MSI-6380 mobo w/updated VIA chip and BIOS
Athlon 1333 (fsb133)
when i first run Sandra and tested memory benchmarks i had about 550..very small output compare to other systems which sandra has in display...so i updated my bios and via chip set...i dont know what else i did but when i rebooted my pc and checked my memory bench...i had 1400..this was very good compare to other systems....that was about a month ago...now few days ago i checked sandra and checked memory bench..i have 550 again...also with cpu arythmetic/logic and multimedia benchmarks they were the same alllll the time...i try to overclock cpu to 1450 and i get 580 in memory, so not a big difference....i plan on buying another stick of memory 256 or even 512 before they get more expensive from Crucial.com....this really bothers me...any suggestions..thanks..

UPDATE>>>>>>>>>>>>
i enabled SDRAM 1T COMMAND in bios
overclocked cpu to 1450mhz
load high performance settings in bios
outcome=800 to 910 (best tests)

when i run the test and check the "Field window" and go to Test Statistics-Array memory used i have 128MB....this means sandra is testing only 128?????
what the hell could be wrong

thanks