Windows XP freeze/hangup

Windows XP Pro: 512K Athlon 64 3200:

I have my hard drive partitioned for XP Home, XP Pro, Programs and Misc. files (Data). It has been working fine for over six months. The original default was XP Pro, (The computer came with XP Home and I duplicated the partition which I upgraded to XP Pro from an upgrade disk) Recently the XP Pro partition freezes (Mouse and keyboard freeze at window for entering password. The cursor is flashing in the password entry window.
I have tried many things including spyware checks, viruses and use of the recovery console (chkdsk /r) and Partition Manager to check. I also changed the default to XP Home, which works fine. The freeze also occurs in safe mode.