K7S5A Boot Problem

recently i upgraded my motherboard from a PIII Tyan, to an ECS K7S5A. Windows XP home was still installed on the HDD from before, so i expected it to boot up. But, instead, what happened was that it would POST fine, but the very first time, it just restarted, no HDD powercycle, jsut POSTed again after that, it would come to the "windows did not start properly" screen, and i would select to start normally, but agian, no errors, just restarted. again.. and again... and agan. i tried safe mode, and it stopped loading at WINDOWS\System32\giveio.sys and rebooted. no erors. please help! Other info--- AMD Athlon XP +1500, 512MB Samsung, 512MB Crucial, DDR PC266, ATi Radeon 9600SE AGP4x, SB Live! Platinum, Western Digital WD307AA 30GB HDD (secondary) Maxtor Diamondmax plus9 6y160po (primary/windows/PageFile) Please help Me! Also, when i tried to boot it into DOS it came up with an error saying, HIMEM.sys Cannot Control Adress Line A20"