1. Windows Advanced Options Menu. Tap the F8 key about once per second or faster as you power up the system. I'm expecting the following menu to appear:
o Safe Mode
o Safe Mode with Networking
o Safe Mode with Command Prompt
o Enable VGA Mode
o Last Known Good Configuration
o Debugging Mode
o Enable Boot Logging
o Starts Windows Normally
o Reboot
o Return to OS Choices Menu

If you get a boot DEVICE menu see: what genius decided F8 should be device boot menu

2. Last Known Good Configuration. Selecting this item will load the registry settings for your last successful login. Not sure if your previous login attempts counted as success. Give it a try. You can use your normal user account with this OPTION. Safe Mode logins do not count (so you can go back to your last successful normal login settings).

3. Safe Mode. Try to boot into Safe Mode. You may be asked to enter the "Administrator" password. If this is Windows XP Home Edition, it may be "blank", as in never set. Either leave the password field blank (for no password) or enter the correct password. Hit 'OK" to continue.

If you can't get past the password request, Safe Mode may be closed to you.

4. Let us know whether "Last known configuration" helps or whether you can boot into Safe Mode with or without the error messages you're getting.Try this from How do get the taskbar and desktop back if Explorer crashes:
Quote

* Close all visible Windows Explorer windows. Other running applications can be LEFT alone.
* Press Ctrl-Alt-Del, and then click Task Manager.
* In the Windows Task Manager application that appears, select New Task (Run) from the File menu.
* Type Explorer and click Ok.