WIndows XP logon....

While in that screen hit CTRL-ALT-DEL all at the same time. If XP is not locked up it should bring up the login screen. If it does not. REBOOT and while the pc is booting keep hitting the F8 key, it should bring up a boot menu with choices, choose SAFE MODE , see if that can get you in to fix what you broke.

What did you click? can you tell us more about what you were doing before it broke?

 

If you choose SAFE MODE (NOT safe mode command prompt only) you should boot up to your desktop in low res. maby you can Re-Run that "advanced system optimizer software" and put that check mark back. Then reboot normally? I dont use that program so its hard to say what removing that check did. Holding the shift key down while booting XP skips the startup folder. Network Admins like to dissable that feature so users cant skip programs he wants to run at every bootup. The program you used that tried to remove that feature may have done some other dammage. Maby email the people that wrote it tell them what you did, they may have a quick fix.

Good Luck....