I replaced mother board now I can't access files on...

My old eMachines mother board died , so I replaced it with a new one it is a
PCCHIPS M848A (v5.0) , SiS 746 socket A ,w/ a AMD Athlon XP 2100 cpu . I initially reconnected every thing to the new mother board , but the computer will not recognize my new mother board .
I then removed he old HD , installed a temp , realized my old back up disc , was a bundled OEM disc which will not recognize my new mother board either , so I went and replaced the old XP Home Bundled restore disc , and bought XP Pro to get the computer basically running .
I then installed my old HD as a slave drive , and the temp as Master .
Now I am being told access denied , I was set up as computer administrator and had my account password protected , is there anyway I can regain , old software , settings , and files ?