my computer dosen't start in normal mode./.. It starts only in safe mode!

when i try to start it from normal mode I get a blue screen saying ... " STOP: c000021a {Fatal System Error} The Windows Logon Process system process terminated unexpectedly with a status of 0xc00000005a (0x00000000 0x0000000)
The system has been shutdown.
"

(then I worked in safe mode(and still I'm working in safe mode))I downloaded about 5 different registry fix software but none of them managed to fix this problem

some one please help!!
{fatal system error}

thanx a lot!

cpu type : Intel pentium 4...
OS Info : windows xp home edition service pack 2