Sounds like a password on POST problem.Try clearing CMOS but if that does not work IBM's fix is :-
Quoting from the ThinkPad 600/600E (2645) Hardware Maintenance Manual:
How to Remove the Power-On Passwords
If only the power-on password is set, do the following to
remove the power-on password.
1. Power off the computer
2. Remove the DIMM cover on the bottom side of the
3. Short-circuit the two password pads or put the
For the location of the password pads or jumper, see
the “Locations” section for each model.
4. Under the short-circuit condition, power on the
computer and wait until the POST ends.
After the POST ends, the password prompt does not
appear. The power-on password is removed.
5. Reinstall the DIMM cover.
If both the power-on password and the supervisor
password are set, do the following to remove the
1. Power on the computer by pressing and holding F1.
2. Enter the supervisor password. The Easy-Setup
3. Click on the Password icon.
4. Click on the Power on icon.
5. Enter the supervisor password and press the Space
6. Press Enter twice.
7. Click on Exit; then click on Restart.
The power-on password has been removed.