Hello, try this:
1) Boot into safe mode.
2) Type into the start menu (or run in Windows XP) "msconfig".
3) On the first tab, select "Normal Startup".
That should ensure a normal boot process and not a selective one.
If I am not mistaken you don't need networking to do that.If you're able to login to safe mode with networking, go so system restore.
restore to date prior to problem and reboot after prompted.