How do I fix Windows XP logging off after log on?

My computer appears to boot normally showing the Windows XP splash window.  It reaches the "Log On To Windows" screen where I key in the User Name and Password.  I click on "OK".  The computer goes to "Please wait . . . loading personal settings."  But it then immediately goes to "Logging off" and returns to the "Log On To Windows" screen.  I had previously removed the hard drive and scanned it with another computer because of the large amount of Trojans, BHO's and Malware that was on it.  It was after the scanning and removal of the Trojans, BHO's and Malware and replacement of the hard drive back into the computer that this occurred.  Can anyone tell me what I need to do to get my computer to boot to the desktop?